Explore all biases

Status quo bias is our tendency to prefer things to remain as they are, even when change would objectively be better. Existing choices or situations feel safer and less risky than alternatives, simply because they are familiar.

Confirmation bias is the tendency to search for, interpret, and remember information in ways that confirm what we already believe. We give more weight to evidence that supports our view, and overlook or downplay what contradicts it.

The availability heuristic is a cognitive shortcut our minds use to assess the frequency or probability of an event. This is achieved by substituting a complex statistical question with a simpler one: instead of asking "How often does this happen?", we ask, "How easily do examples come to mind?". The fluency of retrieval becomes a proxy for frequency. This mental substitution was first extensively documented by psychologists Amos Tversky and Daniel Kahneman in the 1970s. They framed it not as a cognitive flaw, but as a generally efficient and adaptive strategy. In most everyday circumstances, events that occur frequently are indeed easier to recall. The heuristic only becomes a systematic bias when factors unrelated to actual frequency—such as an event's dramatic character, its emotional intensity, or its recentness—make certain memories disproportionately accessible. This mismatch between retrieval fluency and objective frequency is the source of predictable errors in judgment.

Anchoring bias is the tendency to rely too heavily on the first piece of information encountered (the "anchor") when making judgments or decisions. Even when the anchor is irrelevant or arbitrary, it strongly influences subsequent evaluations. Once an anchor is set, people tend to adjust away from it insufficiently.

Adjustment bias is the tendency to make insufficient adjustments away from an initial reference point when estimating values, probabilities, or outcomes. It often operates alongside anchoring bias, where people start from an initial value and fail to adjust far enough from it. Even when individuals recognize that the starting point is flawed or arbitrary, their corrections tend to be inadequate.

The affect heuristic is the tendency to rely on emotional responses and immediate feelings when judging risks, benefits, and probabilities, rather than engaging in deliberate analysis. When something feels good, it is often perceived as less risky and more beneficial; when it feels bad, it is seen as more dangerous. In this heuristic, the question "How do I feel about it?" replaces "What do the facts and probabilities suggest?".

The Dunning-Kruger effect describes how people with low competence in an area often overestimate their own ability, while experts may underestimate themselves. The less you know, the less you understand what you don't know.

Ambiguity aversion describes the robust human tendency to favor options with known probabilities over those with unknown probabilities. This constitutes a preference for risk over uncertainty. Risk involves a known distribution of outcomes—for instance, a 50/50 chance of winning or losing. Ambiguity, by contrast, involves missing information about this distribution; the odds themselves are obscure. First formalized by the economist Daniel Ellsberg, the phenomenon reveals that our choices are not based solely on the potential outcomes, but also on the quality and completeness of the information we possess. The psychological mechanism appears to stem from a deep-seated discomfort with the unknown. When probabilities are incalculable, our capacity for rational analysis and prediction is undermined, creating a feeling of cognitive strain and perceived incompetence. We are often willing to pay a premium to avoid this state of informational helplessness, gravitating toward options where we can at least quantify the dangers. Choosing a known risk, even a poor one, provides a comforting illusion of agency, whereas facing ambiguity confronts us with the stark limits of our knowledge.

Authority bias is the tendency to attribute greater accuracy and weight to the opinions or decisions of an authority figure, regardless of the actual quality of the evidence or reasoning. People assume authorities know best, even when they may be wrong.

Automation bias is the tendency to over-rely on automated systems and algorithms, leading people to overlook errors, limitations, or contradictory information. Complex decisions make people more likely to assume that "the system knows best."

The backfire effect occurs when corrective information strengthens a person's mistaken beliefs rather than weakening them. When deeply held views are challenged, resistance can increase instead of decrease.

The bandwagon effect is the tendency to adopt beliefs, behaviors, or attitudes because many others are doing so. Popularity is interpreted as a signal of correctness or value.

Base rate neglect is the tendency to ignore general statistical information (base rates) in favor of specific, often vivid information, leading to systematic errors in probability judgments.

Belief bias is the tendency to judge the strength or validity of an argument based on whether we agree with its conclusion, rather than on the quality of the logic leading to it. Arguments that align with existing beliefs are perceived as stronger, even when the reasoning is flawed.

The bias blind spot, first documented by Emily Pronin, Daniel Lin, and Lee Ross at Princeton (2002), is the meta-cognitive tendency to recognize the influence of cognitive biases on other people's judgments while failing to see—or actively denying—the same influence on our own. It is, in essence, a bias about bias. The effect is robust across domains: people acknowledge that advertising sways others but insist it does not affect their own purchasing; they concede that political ideology colors others' interpretation of facts but believe their own views are purely evidence-based. Crucially, the bias blind spot is not reduced by intelligence or expertise—in fact, higher cognitive ability sometimes amplifies it, because smart people are better at constructing sophisticated justifications for their own objectivity.

Choice overload—also known as the paradox of choice, a concept popularized by psychologist Barry Schwartz (2004) and demonstrated in Sheena Iyengar and Mark Lepper's famous 'jam study' (2000)—is the phenomenon whereby an abundance of options, rather than empowering decision-makers, leads to decision avoidance, lower satisfaction, and greater regret. When faced with too many alternatives, the cognitive cost of evaluating them exceeds the benefit of having more options. The effect is strongest when options are difficult to compare, consequences are significant, and there is no clear 'best' choice. Choice overload challenges the economic assumption that more options always increase welfare.

The clustering illusion is the tendency to perceive meaningful patterns or clusters in random data, even when the apparent structure arises purely by chance. First described by Thomas Gilovich in his 1991 book *How We Know What Isn't So*, the bias reflects our deep-seated need for order: the human brain is an extraordinary pattern-detection machine, honed by evolution to spot regularities that signal food, threats, or social alliances. However, this same machinery misfires in data-rich modern environments, causing us to 'see' trends in stock charts, streaks in sports, or cancer clusters on maps that are entirely consistent with random variation. Statisticians call this apophenia — the perception of connections in unrelated things.

Cognitive dissonance is the psychological discomfort that arises when a person holds conflicting beliefs, attitudes, or behaviors. To reduce this discomfort, people often change their attitudes or reinterpret information rather than change their behavior.

Conservatism bias is the tendency to update beliefs too slowly as new data arrive. Mechanistically, people underweight the likelihood carried by fresh evidence relative to their prior due to cognitive inertia, anchoring on initial estimates, and the reputational or self-justification costs of admitting error. In sequential environments this produces a systematic lag behind a changing reality.

The contrast effect is the tendency for a judgment to be displaced away from the properties of nearby options or recent stimuli. Because perception and value are encoded relatively—via normalization, adaptation levels, and range–frequency coding—the reference frame shifts with context, making the same target look better or worse depending on what surrounds or precedes it. As a result, evaluations become context-dependent rather than absolute.

The default effect is the tendency to accept a preselected option because it minimizes cognitive effort and feels safe under uncertainty. It is driven by three reinforcing mechanisms: tiny frictions to switch, perceived endorsement by the choice architect, and loss aversion that makes deviation feel like giving something up. In addition, inaction often carries less perceived responsibility than action, further tilting choices toward the default.

The denomination effect is a cognitive bias where individuals are more likely to spend money when it is in smaller denominations compared to a single large denomination of equivalent value. The form in which currency is presented, rather than its objective value, significantly influences spending decisions. Smaller units—whether coins, small bills, or fragmented digital credits—are psychologically coded as less valuable and more expendable. The core mechanism behind this phenomenon is the "pain of paying," a concept describing the psychological discomfort experienced when parting with money. A large, high-value bill represents a significant, coherent whole. The act of "breaking" it for a minor purchase feels disproportionate and wasteful, creating a psychological hurdle. This single unit is perceived as having a qualitative integrity that makes its expenditure feel more consequential. In contrast, smaller denominations are seen as more fungible and already designated for transactional purposes, thereby reducing the friction and cognitive load associated with spending them.

Distinction bias is the tendency to overestimate how much small, quantifiable differences matter when options are evaluated side by side, relative to when they are experienced on their own. Joint evaluation makes easily comparable attributes (inches, megapixels, speed) unusually salient and overweighted. After the choice, context, habit, and adaptation dominate, so experienced utility becomes far less sensitive to those differences.

Duration neglect is the systematic tendency to ignore or heavily underweight how long an experience lasts when forming retrospective evaluations. Demonstrated in Daniel Kahneman's landmark colonoscopy studies (Redelmeier & Kahneman, 1996), patients who endured a longer but gradually easing procedure rated their overall experience more favourably than those with a shorter but abruptly ending one — even though the longer group experienced objectively more total pain. The finding reveals a fundamental feature of the 'remembering self': our autobiographical memory compresses experiences into snapshots defined by peak intensity and final moments, essentially discarding duration information.

Effort justification is a specific form of cognitive dissonance reduction in which people assign greater value to outcomes they worked hard to achieve, regardless of the outcome's objective quality. The phenomenon was first demonstrated by Elliot Aronson and Judson Mills (1959): participants who underwent a severe initiation to join a boring discussion group rated the group significantly more interesting than those who underwent a mild initiation. The mechanism is straightforward — if I suffered for something and it turns out to be worthless, I face painful dissonance; the easiest resolution is to inflate the outcome's perceived value. This creates a self-reinforcing loop: the more effort invested, the harder it becomes to see the result clearly.

The empathy gap — formally the 'hot–cold empathy gap' — is the systematic failure to predict how visceral states (hunger, pain, anger, sexual arousal, craving) alter preferences and behaviour. Coined by George Loewenstein (1996, 2005), research shows the gap operates in both directions: in a 'cold' (calm) state, people dramatically underestimate how they will behave when 'hot' (emotionally aroused), and vice versa. In one striking study, young men in a calm state predicted they would never engage in risky sexual behaviour — but when aroused, their stated willingness roughly doubled. The empathy gap is not merely about empathising with others; it is fundamentally about our inability to empathise with our own future selves in different emotional states.

The endowment effect is the tendency to assign higher value to things simply because we own them. Ownership increases reluctance to give something up, even when we would not pay the same amount to acquire it.

Escalation of commitment is the tendency to continue investing time, money, or resources into a failing course of action because of prior investments, rather than evaluating future costs and benefits objectively.

The false consensus effect is the tendency to overestimate how widely one's own beliefs, attitudes, and behaviours are shared by others. First demonstrated by Lee Ross, David Greene, and Pamela House (1977) in the classic 'sandwich board' experiment — where students who agreed to walk around campus wearing an advertising sign estimated that 62% of peers would also agree, while those who refused estimated only 33% would agree — the bias reflects a fundamental egocentric anchoring process. We use our own perspective as the primary data point and insufficiently adjust for the diversity of others' views. The effect is amplified by selective exposure: we surround ourselves with like-minded people, which makes our views seem more representative than they are.

The familiarity heuristic is a decision rule that treats recognition and processing fluency as cues to likelihood, value, or safety. When faced with two options and only one is recognised, a single recognition cue can suffice to choose it — a strategy that is ecologically rational where familiarity correlates with quality. The mechanism is affective and automatic: information that is easier to retrieve feels truer and safer, reducing cognitive effort. In information-dense environments, however, familiarity can be manufactured via repetition and exposure, decoupling it from genuine merit.

The framing effect is the systematic tendency to reach different conclusions from logically identical information depending on how it is presented. Demonstrated definitively by Amos Tversky and Daniel Kahneman (1981) in the 'Asian disease problem,' participants chose a sure option when outcomes were framed as lives saved (gain frame) but gambled when the same outcomes were framed as deaths (loss frame) — even though the expected values were identical. Prospect Theory explains the mechanism: people are risk-averse in the domain of gains and risk-seeking in the domain of losses, so the frame determines the perceived domain and thus the preference. The effect is remarkably robust across cultures, education levels, and expertise — even trained statisticians are susceptible.

Functional fixedness is a cognitive bias that limits a person to seeing objects, tools, or processes only in their conventional roles, blocking creative problem-solving. First identified by Karl Duncker (1945) through the famous 'candle problem' — where participants struggled to attach a candle to a wall using only a box of tacks and matches, failing to see the box as a shelf rather than a container — the bias reveals how strongly prior experience shapes our perception of possibility. Functional fixedness increases with expertise and experience: the more you have used something in one way, the harder it becomes to reconceive its function. Neuroscience research suggests the effect involves automatic activation of learned associations in the prefrontal cortex, which must be actively inhibited for creative insight to occur.

The gambler's fallacy is the mistaken belief that random, independent events should 'even out' over the short run – that after a streak of similar outcomes, the opposite result becomes more likely. The fallacy arises from a deep-seated human intuition that randomness should look balanced, even over small samples. First formally described in studies of probability cognition, it reflects a confusion between the law of large numbers (which describes long-run convergence) and short-run expectations. In reality, each independent event – a coin flip, a roulette spin, a dice roll – carries exactly the same probability regardless of what happened before.

Groupthink is the tendency of groups to prioritize consensus and harmony over critical evaluation, leading to poor decision-making as alternatives and risks are insufficiently explored.

The halo effect is a cognitive bias whereby a single positive (or negative) trait of a person, product, or brand disproportionately colors the overall evaluation of that entity across unrelated dimensions. First identified by psychologist Edward Thorndike in 1920 through his research on military officer evaluations, the halo effect reveals that our judgments rarely operate in isolation – instead, a strong impression in one area 'radiates' outward, influencing assessments of completely independent qualities. When we find someone attractive, we unconsciously assume they are also intelligent, kind, and competent. When a brand delivers one great product, we assume everything they make is excellent.

Hindsight bias – often called the 'knew-it-all-along' effect – is the tendency to perceive past events as having been more predictable than they actually were. Once we know an outcome, our memory unconsciously reconstructs the past to make that outcome seem inevitable, and we overestimate how well we could have predicted it beforehand. First systematically studied by Baruch Fischhoff in the 1970s, the bias operates through three mechanisms: memory distortion (misremembering our original predictions), inevitability perception (feeling the outcome was bound to happen), and foreseeability judgment (believing we personally could have predicted it).

The hot-hand fallacy is the belief that a person who has experienced a streak of success in a random or semi-random process has a greater probability of continued success in subsequent attempts – that they are 'on fire' or have a 'hot hand.' Originally studied by Thomas Gilovich, Robert Vallone, and Amos Tversky in their landmark 1985 paper on basketball shooting, the researchers found that players' sequential shot outcomes were statistically independent: a made basket did not predict the next shot any better than chance. Despite this, players, coaches, and fans overwhelmingly believed in the hot hand. The finding became one of the most debated results in behavioral science, with later research suggesting a small hot-hand effect may exist in some contexts – but far weaker than people's intuitions suggest.

The illusion of control is the tendency to believe we can influence outcomes that are actually determined by chance, external forces, or complex systems beyond our reach. First described by psychologist Ellen Langer in 1975, the bias emerges when situations contain cues associated with skill-based tasks – personal involvement, choice, competition, familiarity – even when the outcome is entirely random. Langer demonstrated that people would pay more for lottery tickets they chose themselves than for randomly assigned ones, and would be less willing to trade 'their' ticket, as though personal selection increased their probability of winning. The illusion of control serves a deep psychological need: feeling in control reduces anxiety and promotes action, but it also leads to poor risk assessment and overcommitment to failing strategies.

The illusory truth effect is the cognitive phenomenon whereby repeated exposure to a statement increases our perception of its truthfulness – regardless of whether it is actually true. First demonstrated by Lynn Hasher, David Goldstein, and Thomas Toppino in 1977, the effect operates through processing fluency: repeated statements are processed more easily by the brain, and this ease of processing is unconsciously interpreted as a signal of truth. The effect is remarkably robust – it works even when people are explicitly warned about it, even when the repeated claim contradicts their existing knowledge, and even when the source is known to be unreliable. In an era of information overload and algorithmic amplification, the illusory truth effect has become one of the most consequential cognitive biases.

Impact bias is the systematic tendency to overestimate both the intensity and duration of our emotional reactions to future events – positive or negative. Coined by Daniel Gilbert and Timothy Wilson through their research on 'affective forecasting,' the bias reveals a fundamental flaw in how we predict our own emotional futures. We imagine that winning a promotion will bring lasting euphoria, that losing a job will create enduring misery, or that moving to a sunny climate will permanently boost happiness. In reality, the human psychological immune system is remarkably effective at restoring emotional equilibrium – a process called hedonic adaptation. The impact bias persists because we focus narrowly on the anticipated event while ignoring the many other experiences, routines, and relationships that will continue to shape our daily emotional lives.

Information bias is the tendency to seek, gather, and value additional information even when it cannot possibly improve the quality of a decision – and may actually worsen it through delay, confusion, or false confidence. The bias reflects a deep human intuition that 'more information is always better,' but research consistently shows that beyond a certain threshold, additional data does not improve decision accuracy and can even degrade it by introducing noise and complexity. In medical diagnosis, business strategy, and everyday choices, the compulsion to gather 'just a little more' information often delays action, increases costs, and creates analysis paralysis without producing better outcomes.

In-group bias is the tendency to systematically favor members of one's own group – whether defined by nationality, workplace, alma mater, sports team, or even arbitrary assignment – while viewing outsiders with greater suspicion or indifference. This favoritism operates automatically and often unconsciously: we attribute better motives, greater competence, and more trustworthiness to 'our' people, while simultaneously discounting the contributions and character of those outside the group.

The introspection illusion is the mistaken belief that we have direct, reliable access to the causes of our own thoughts, feelings, and decisions. We believe we know why we do what we do – but research shows that much of our mental processing occurs outside conscious awareness. At the same time, we assume other people lack this self-insight, and that their actions are driven more by biases, emotions, or external pressures. The result is an asymmetry where we overestimate our own rationality while underestimating others'.

The just-world hypothesis is the deeply ingrained belief that the world is fundamentally fair – that good things happen to good people, and bad things happen to those who deserve them. This cognitive bias serves as a psychological defense mechanism: if the world is just, then we can feel safe as long as we behave well. The cost, however, is that we tend to blame victims for their misfortune and attribute success entirely to merit, ignoring the powerful roles of circumstance, structural inequality, and randomness.

The law of small numbers is the mistaken belief that small samples are as representative of reality as large ones. We draw strong conclusions from limited data and systematically underestimate how much randomness affects small samples. The name is an ironic twist on the 'law of large numbers' in statistics, which states that large samples yield reliable estimates – something small samples decidedly do not.

Loss aversion is the tendency to experience losses as more psychologically impactful than equivalent gains. Losing something feels worse than gaining the same thing feels good.

The mere exposure effect – also known as the familiarity principle – is the psychological phenomenon whereby people develop a preference for things simply because they have been exposed to them repeatedly. Discovered by Robert Zajonc in a series of landmark studies in 1968, the effect operates below conscious awareness: we don't realize that our increased liking is caused by familiarity rather than genuine quality assessment. Zajonc demonstrated the effect using Chinese characters, nonsense words, faces, and geometric shapes – in every case, items shown more frequently were rated as more pleasant, attractive, or trustworthy. The effect is one of the most robust findings in psychology, replicated across cultures, ages, and stimulus types, and it operates even when people don't consciously remember having seen the stimuli before (subliminal mere exposure).

Moral licensing (also called the licensing effect) is the psychological phenomenon whereby performing a virtuous act – or even just imagining or intending one – grants people unconscious 'moral credit' that they then spend on subsequent behavior that is less ethical, less healthy, or less aligned with their stated values. First systematically studied by Benoît Monin and Dale Miller in 2001, the effect reveals that morality functions less like a consistent character trait and more like a mental bank account: good deeds create a surplus that people feel entitled to draw down. The effect is particularly insidious because it is unconscious – people who display moral licensing genuinely believe their subsequent behavior is justified, not that they are 'cheating.'

Negativity bias is the well-documented tendency for negative events, emotions, and information to exert a disproportionately stronger psychological impact than equivalently positive ones. Research by psychologists Paul Rozin and Edward Royzman (2001) established that 'negative events are more salient, potent, dominant in combinations, and generally more impactful than positive events.' This asymmetry shapes attention, memory, learning, and decision-making: losses loom larger than gains, bad impressions form faster than good ones, and negative feedback is remembered more vividly and longer than praise. The bias operates across virtually all domains of human cognition — from interpersonal relationships to financial decisions to political attitudes.

Normalcy bias is a cognitive tendency that causes people to underestimate both the likelihood and the severity of a disaster or unprecedented event. Because the brain uses past experience as its primary reference for predicting the future, situations that have 'never happened before' are mentally assigned near-zero probability — even when clear warning signs are present. Research by disaster psychologist Amanda Ripley and others shows that during emergencies, a significant portion of people (estimated 70–80%) initially freeze or continue routine behavior rather than taking protective action. Normalcy bias is not mere denial; it reflects genuine difficulty in processing information that falls outside the range of previous experience.

Omission bias is the systematic tendency to judge harmful actions as morally worse than equally harmful omissions (failures to act). People perceive 'doing something' that causes harm as more blameworthy than 'not doing something' that causes the same or even greater harm. This asymmetry was formalized by psychologist Jonathan Baron, who demonstrated that people evaluate identical outcomes differently depending on whether they resulted from commission or omission. The bias is rooted in the intuition that causing harm through action implies intent and personal responsibility, whereas harm through inaction feels accidental or unavoidable — even when the decision not to act was deliberate.

Optimism bias is the pervasive tendency to overestimate the probability of positive future events and underestimate the probability of negative ones, particularly regarding oneself. Neuroscientist Tali Sharot's research has shown that approximately 80% of people exhibit optimism bias, making it one of the most prevalent cognitive biases. The bias operates through selective updating: when people receive information suggesting the future is better than expected, they readily incorporate it into their beliefs; when they receive information suggesting worse outcomes, they partially discount it. Neuroimaging studies reveal that optimism bias is associated with reduced activity in the right inferior frontal gyrus — a brain region involved in processing negative information — when people consider their personal future.

Outcome bias is the tendency to evaluate the quality of a decision based on its eventual outcome rather than on the quality of the reasoning and information available at the time the decision was made. Psychologist Jonathan Baron first systematically studied this bias, demonstrating that people rate identical decision processes differently depending on whether the outcome was positive or negative. This creates a fundamental problem for learning and accountability: good decisions that happen to produce bad results (due to inherent uncertainty) are unfairly punished, while poor decisions that happen to produce good results (due to luck) are unfairly rewarded. In probability-rich domains like medicine, investing, and strategy, outcome bias systematically distorts feedback and prevents accurate assessment of decision-making skill.

Overconfidence bias is the systematic tendency to overestimate one's own abilities, knowledge, predictions, or degree of control over outcomes. It manifests in three distinct forms: overestimation (thinking you perform better than you actually do), overplacement (believing you are better than others – the 'above average' effect), and overprecision (being too certain that your beliefs are correct, expressed as overly narrow confidence intervals). Together, these forms make overconfidence one of the most pervasive and consequential cognitive biases. Daniel Kahneman has called overconfidence 'the most significant of the cognitive biases' because of its role in poor decision-making at every level.

The planning fallacy is the systematic tendency to underestimate the time, costs, and risks required to complete a task or project – even when we have direct experience with similar tasks that took longer than expected. First identified by Daniel Kahneman and Amos Tversky in 1979, the fallacy occurs because we plan based on an idealized 'inside view' of the specific project (imagining the best-case scenario) rather than the 'outside view' of how similar projects have actually performed. The result is chronic optimism that persists despite repeated evidence to the contrary.

Present bias is the tendency to give disproportionate weight to immediate rewards and costs relative to those occurring in the future – even when waiting would produce objectively better outcomes. Unlike simple impatience, present bias involves a specific inconsistency: we make plans for our future selves that we systematically fail to follow when the future becomes the present. Today, we sincerely intend to start exercising tomorrow, to save next month, or to begin the report next week – but when 'tomorrow' arrives, the immediate cost of action looms large again, and we postpone once more.

The primacy effect is the tendency for information encountered early in a sequence to carry disproportionate weight in subsequent judgments, evaluations, and memory. First impressions don't just matter – they create a lens through which all later information is filtered. Once an initial impression forms, we tend to interpret ambiguous subsequent information in ways that confirm it, and we are slow to update even when contradictory evidence accumulates. The primacy effect is one component of the broader serial position effect, which describes how position in a sequence affects recall and influence.

The priming effect is the tendency for exposure to certain words, images, ideas, or stimuli to unconsciously influence subsequent thoughts, feelings, and behaviors.

Probability neglect is the cognitive tendency to focus almost entirely on the magnitude or vividness of a potential outcome while ignoring or heavily discounting its actual probability. Legal scholar Cass Sunstein, who coined and extensively studied the term, demonstrated that when outcomes are emotionally charged — particularly when they involve dread, outrage, or excitement — people essentially treat low-probability events as if they were certain to occur. This is not a failure of mathematical understanding but rather an emotional override: the affect heuristic generates a strong feeling about the outcome, and that feeling substitutes for careful probabilistic reasoning. Probability neglect explains why people simultaneously overspend on lottery tickets (vivid positive outcome) and overreact to terrorism risks (vivid negative outcome), even though both have negligible probabilities.

Projection bias is the tendency to project our current emotional state, preferences, and desires onto our future selves and onto other people – assuming that how we feel right now is how we will feel later, and how others feel too. We understand intellectually that feelings change, but we systematically underestimate how much they will change. The result is decisions made for a future self whose tastes, needs, and circumstances will differ from what we imagine today.

Psychological reactance is the motivational state that arises when people perceive their freedom of choice to be threatened, restricted, or eliminated. Rather than complying, they experience an intense urge to restore the threatened freedom – often by doing the exact opposite of what is being requested. Reactance is not simple stubbornness; it is a deep psychological response rooted in the fundamental human need for autonomy. The stronger the perceived threat to freedom, the more intense the reactance, and the more likely the person is to boomerang toward the forbidden option.

Recency bias is the tendency to give disproportionate weight to the most recent information, events, or experiences when making judgments and predictions – at the expense of earlier, potentially more representative data. Our memories are not democratic: recent events are vivid, emotionally accessible, and easy to recall, while older information fades into an undifferentiated background. The result is that our perception of reality is systematically skewed toward whatever happened last, regardless of whether it is more informative than what came before.

The representativeness heuristic, identified by Daniel Kahneman and Amos Tversky in their groundbreaking 1972 research, is the mental shortcut of judging the probability of an event or category membership based on how closely it resembles a typical case (prototype) rather than on actual statistical likelihood. When something 'looks like' or 'feels like' a member of a category, we assign it a high probability of belonging to that category — regardless of base rates, sample sizes, or other relevant statistical information. This heuristic is efficient in many everyday situations but produces systematic errors when similarity and probability diverge, which happens more often than people realize.

Risk compensation (also called the Peltzman effect, after economist Sam Peltzman) is the tendency for people to adjust their behavior in response to perceived changes in risk – taking greater risks when they feel more protected and being more cautious when they feel exposed. The critical insight is that safety measures do not simply reduce risk; they also change behavior, sometimes partially or fully offsetting the intended safety benefit. People maintain a subjective 'target level of risk' and unconsciously adjust their actions to stay near it.

Salience bias is the tendency to focus on information, events, or attributes that are emotionally striking, novel, or visually prominent — and to give them disproportionate weight in judgments and decisions. What stands out most is not necessarily what matters most, but the brain treats it as if it does.

Scarcity bias is the cognitive tendency to assign greater value to things that are perceived as rare, limited, or dwindling in availability — often independent of their actual utility. When something becomes scarce, our desire for it intensifies, and we perceive it as more valuable than when it was abundant. The psychological mechanism was famously demonstrated by Worchel, Lee, and Adewole (1975) in their cookie jar experiment: participants rated cookies as more desirable and tasty when only two remained in the jar compared to when ten were available — even though the cookies were identical. Robert Cialdini identified scarcity as one of the six fundamental principles of persuasion in his landmark work 'Influence' (1984), noting that the fear of missing out is often a more powerful motivator than the prospect of gaining something new.

Self-serving bias is the systematic tendency to attribute positive outcomes to one's own character, skills, and effort (internal attribution) while blaming negative outcomes on external factors beyond one's control (situational attribution). This asymmetric pattern of causal explanation protects self-esteem and maintains a positive self-image. First extensively documented by Miller and Ross (1975), the bias has been replicated across cultures — though its strength varies. In individualistic Western cultures, self-serving attributions are stronger than in collectivistic Eastern cultures, where self-effacing tendencies partially counterbalance them. Neuroimaging studies suggest the bias involves the medial prefrontal cortex, which processes self-relevant information, and the anterior cingulate cortex, which monitors conflicts between reality and desired self-image.

Social desirability bias is the systematic tendency to present oneself in a favorable light by over-reporting socially approved behaviors and under-reporting socially disapproved ones. It affects both self-report surveys and face-to-face interactions, distorting data and interpersonal communication in predictable ways. Edwards (1957) first formalized the concept, and Crowne and Marlowe (1960) developed the widely used Marlowe-Crowne Social Desirability Scale to measure individual differences in the tendency. The bias operates on two levels: impression management (deliberate self-presentation to others) and self-deception (unconsciously believing one's own inflated self-image).

Stereotyping is the cognitive process of assigning traits, abilities, or behaviors to individuals based on their perceived group membership rather than their actual individual characteristics. While categorization itself is a normal and necessary cognitive function — the brain processes roughly 11 million bits of sensory information per second and must simplify — stereotyping becomes problematic when these simplified mental models override evidence about specific individuals. Gordon Allport's 'The Nature of Prejudice' (1954) laid the groundwork for understanding stereotyping as a cognitive shortcut that can lead to prejudice. Modern research distinguishes between explicit stereotypes (conscious beliefs) and implicit stereotypes (automatic associations measured through tools like the Implicit Association Test developed by Greenwald et al., 1998), which can influence behavior even when people consciously reject stereotypical thinking.

Survivorship bias is the tendency to focus on individuals or outcomes that made it through a process while overlooking those that failed, leading to distorted conclusions about success.

Temporal discounting is the well-documented tendency to assign progressively less subjective value to rewards and consequences as they move further into the future. A reward available today is valued more highly than the same reward available next month, which is in turn valued more than the same reward next year — even when waiting would yield a larger total benefit. Economists traditionally modeled this as exponential discounting (consistent over time), but behavioral research by Ainslie (1975) and Thaler (1981) revealed that humans actually discount hyperbolically — meaning we are especially impatient about short delays but relatively indifferent to differences between long delays. This inconsistency explains why people make plans to save 'starting next month' but never actually begin: when 'next month' arrives, the short-term cost feels much larger than it did from a distance.

The third-person effect, first identified by sociologist W. Phillips Davison in 1983, is the perceptual hypothesis that people tend to believe that persuasive communications — advertising, propaganda, media messages — have a greater effect on others than on themselves. In essence, we see ourselves as discerning and resistant to influence, while assuming 'other people' are gullible and easily swayed. The effect has been robustly replicated across dozens of studies involving different types of media content: political advertising, product marketing, pornography, violent media, fake news, and public health campaigns. Meta-analyses by Paul, Salwen, and Dupagne (2000) confirmed the effect across cultures and demographics. Crucially, the gap between perceived self-impact and perceived impact on others grows larger when the message is perceived as socially undesirable (e.g., propaganda, misinformation).

Trait ascription bias is the tendency to view one's own personality and behavior as highly variable and context-dependent, while perceiving others' personality and behavior as more fixed, predictable, and driven by stable character traits. When someone else is rude, we conclude they 'are a rude person'; when we ourselves are rude, we attribute it to having a bad day. This asymmetry was demonstrated by Nisbett, Caputo, Legant, and Marecek (1973) and is closely related to the fundamental attribution error (Ross, 1977). The underlying mechanism involves differential access to information: we have rich knowledge of the many situations that shape our own behavior, but observe others primarily through their actions — leading us to over-attribute their behavior to dispositional traits. Actor-observer asymmetry research consistently shows this pattern across cultures, though it is most pronounced in individualistic societies.

Truth bias is the default cognitive tendency to assume that other people's statements are truthful. Rather than evaluating each claim on its merits, humans operate with a 'truth default' — we accept information as true unless we encounter specific triggers that activate suspicion. This framework, formalized by Timothy Levine in his Truth-Default Theory (TDT, 2014), explains why humans are surprisingly poor lie detectors despite believing otherwise. Research consistently shows that people's ability to detect deception hovers around 54% — barely above chance — even among professionals like police officers, judges, and customs officials. The reason is not lack of intelligence but rather that truth bias is adaptive: in a world where the vast majority of communications are truthful, defaulting to trust is efficient and enables the social cooperation that complex societies depend on.

Unit bias is the cognitive tendency to perceive a single unit — one portion, one serving, one container, one task — as the appropriate and 'correct' amount, regardless of the unit's actual size. The brain uses 'one' as a natural completion point, creating a sense of satisfaction and closure that is independent of whether the quantity was adequate, excessive, or insufficient. Geier, Rozin, and Doros (2006) demonstrated unit bias experimentally: when free pretzels were offered in a bowl with a serving spoon, people took one spoonful regardless of spoon size — those given a larger spoon ate 33% more without realizing it. The research showed that the 'unit' acts as a powerful implicit suggestion, overriding internal hunger signals and rational portion control.

Zero-risk bias is the strong psychological preference for options that completely eliminate a risk — reducing it to zero — over options that achieve a much larger overall risk reduction but leave some residual risk. The appeal of 'zero' is not proportional; it exerts a unique psychological pull that distorts cost-benefit analysis. The bias was formally demonstrated by Baron, Gowda, and Kunreuther (1993), who showed that people preferred regulatory actions that eliminated a small risk entirely over alternative actions that reduced a much larger risk by a greater absolute amount. The underlying mechanism involves the 'certainty effect' described by Kahneman and Tversky in Prospect Theory: outcomes that are certain (including 'certainly zero risk') are overweighted relative to outcomes that are merely probable, even when the probable outcomes are objectively superior.

The Barnum effect (also called the Forer effect) is the psychological phenomenon where individuals rate vague, generic personality descriptions as highly accurate and uniquely applicable to themselves — especially when they believe the description was created specifically for them. Named after showman P.T. Barnum (attributed the quote 'there's a sucker born every minute'), the effect was empirically demonstrated by psychologist Bertram Forer in 1948. In Forer's original experiment, students took a 'personality test' and were each given the same generic feedback paragraph. They rated it 4.3 out of 5 for accuracy — despite every student receiving identical text. The experiment has been replicated hundreds of times with remarkably consistent results across cultures, age groups, and education levels. The effect is strongest when the description is perceived as coming from an authoritative source, when it contains mostly positive traits, and when the subject has invested effort in the assessment process.

Courtesy bias is the systematic tendency to give overly positive, agreeable, or diplomatically softened responses — particularly in face-to-face interactions — to avoid social discomfort, preserve relationships, or respect perceived power dynamics. Unlike social desirability bias (which also operates in anonymous settings), courtesy bias is specifically activated by interpersonal presence and the immediate social costs of expressing negative views. The bias is especially pronounced in cultures with strong politeness norms (many East Asian and Scandinavian cultures) and in organizational hierarchies where disagreeing with authority carries real or perceived risks. Research in development economics has shown that courtesy bias significantly distorts data from field surveys: respondents in low-income countries often tell interviewers what they think the interviewer wants to hear, leading to systematically inflated program evaluations.

The curse of knowledge is the cognitive bias where individuals who possess knowledge on a topic find it extremely difficult to think about that topic from the perspective of someone who lacks that knowledge. Once you know something, you cannot easily simulate the mental state of not knowing it — and you systematically underestimate how difficult it is for others to understand. The concept was introduced by economists Camerer, Loewenstein, and Weber (1989) and famously demonstrated by Elizabeth Newton's 1990 Stanford doctoral experiment: 'tappers' tapped the rhythm of well-known songs and estimated that 'listeners' would identify 50% of them. In reality, listeners identified only 2.5%. The tappers couldn't unhear the melody playing in their heads, making them dramatically overestimate its transmission.

The decoy effect (also known as the 'asymmetric dominance effect') occurs when the introduction of a third, inferior option — the 'decoy' — systematically shifts preference between two existing options by making one of them appear relatively more attractive. The decoy is designed to be clearly worse than one option (the 'target') but not clearly comparable to the other (the 'competitor'), creating an asymmetric dominance that nudges choice. First described by Huber, Payne, and Puto (1982), the decoy effect violates a fundamental assumption of rational choice theory: the 'independence of irrelevant alternatives' (adding an option nobody would choose shouldn't change preferences between existing options). Yet it reliably does, across consumer goods, political candidates, job applicants, and even mate selection.

The disposition effect is the well-documented behavioral finance phenomenon where investors disproportionately sell assets that have increased in value ('winners') while holding onto assets that have decreased in value ('losers') — even when rational analysis would suggest the opposite strategy. First formally identified by Shefrin and Statman (1985), the effect has been confirmed in virtually every financial market studied, from individual stock trading to real estate. The psychological mechanism combines loss aversion (realizing a loss is painful), mental accounting (each investment is tracked separately rather than as part of a portfolio), and the desire for pride while avoiding regret. Selling a winner provides a burst of pride and confirms the investor's skill narrative; selling a loser forces an admission of error. Odean (1998) found that individual investors are 1.5 times more likely to sell a winning position than a losing one.

Egocentric bias is the tendency to anchor judgments in one's own perspective, memory, and knowledge when interpreting shared events or estimating what others think, know, and feel. The mechanism is accessibility: our own experiences, intentions, and efforts are vividly represented in mind, while other people's are inferred indirectly, so the self-anchor is used as a default reference even when the task calls for an outside view. The result is a systematic overweighting of one's own contribution to joint outcomes, one's own visibility to others, and the degree to which others share one's knowledge, preferences, and emotional reactions. Egocentric bias is not the same as selfishness; it appears in conscientious and well-meaning people and applies to both flattering and unflattering judgments. It overlaps with self-serving bias, the false consensus effect, and the curse of knowledge, but its core is perspectival rather than motivational.

The end-of-history illusion is the tendency to treat the present self as a finished product: people readily acknowledge substantial past change yet predict little change ahead. Mechanistically, they anchor on current preferences, simulate the future sparsely, and are motivated to maintain a coherent identity, so they underweight life events and maturation that reliably reshape beliefs and tastes. Large-sample evidence shows this underprediction is strikingly consistent across ages.

Feedback avoidance is the systematic tendency to actively avoid, delay, or ignore information about one's own performance, health, or standing — even when that information could be valuable for improvement and well-being. The bias reflects a deep tension between the desire for self-improvement (which requires honest feedback) and the desire for self-protection (which avoids potentially threatening information). Sweeny et al. (2010) documented this as 'information avoidance' in health contexts, while organizational psychologists have studied it as 'feedback-seeking reluctance.' The core mechanism involves anticipated negative affect: people avoid feedback not because of the information itself, but because of the emotional pain they expect to feel upon receiving it. Critically, research shows that the anticipated pain almost always exceeds the actual pain — people overestimate how bad negative feedback will feel and underestimate their capacity to cope.

The Forer effect (often used interchangeably with the Barnum effect) is the psychological tendency to rate vague, generalized personality descriptions as highly accurate and uniquely applicable to oneself — particularly when one believes the description was individually crafted. Named after psychologist Bertram Forer, who first demonstrated the effect in 1948, it reveals a fundamental vulnerability in human self-assessment: we are remarkably poor at distinguishing personalized insights from generic statements. Forer gave his students a 'personality test,' then provided each student with the same generic paragraph (actually compiled from a newspaper horoscope column). Students rated the accuracy of their 'personalized' profile at 4.26 out of 5. The effect has been replicated over 100 times with similar results, demonstrating its robustness across cultures, education levels, and assessment contexts. Dickson and Kelly (1985) showed the effect persists even when participants are explicitly warned about it beforehand.

Hyperbolic discounting is the tendency for the subjective value of delayed rewards to drop steeply over short delays and much more shallowly over longer ones. The implied discount rate declines with time, producing a strong premium on immediacy and weak concern for distant outcomes. This declining-rate property generates dynamic inconsistency: options preferred in advance are reversed at the moment of choice.

The identifiable victim effect is a bias whereby a single named person elicits more empathic concern and helping than a large set of anonymous victims. The mechanism hinges on vividness and singularity, which foster mental imagery, personal responsibility, and perceived efficacy ("my help will matter"), while large numbers trigger scope insensitivity and psychic numbing. Providing statistical context can recruit analytical processing that dampens the affective response that drives generosity.

The IKEA effect is the cognitive bias whereby people place disproportionately high value on products, ideas, or solutions they have partially created or assembled themselves — regardless of the objective quality of the result. Named after the Swedish furniture retailer whose business model requires customers to assemble their own furniture, the effect was formally demonstrated by Norton, Mochon, and Ariely (2012). In their experiments, participants who assembled simple IKEA storage boxes were willing to pay 63% more for their self-assembled boxes than for identical pre-assembled ones. Crucially, the effect required successful completion: if participants built something but it was then disassembled before they could admire it, the inflated valuation disappeared. This suggests the effect is tied to the sense of competence and accomplishment that comes from seeing a completed creation, not merely to the effort invested.

Information avoidance is the strategic—often automatic—restriction of attention and search to reduce anticipated negative affect, threats to self-concept, or obligations to act, even when the information would improve decisions. The mechanism is not mere ignorance but an active optimization over information: “not knowing” yields immediate psychological utility by dampening aversive emotions and preserving beliefs and identity. As a result, people choose not to acquire information, contradicting the classical assumption that more information is always better.

The ostrich effect — named after the myth that ostriches bury their heads in the sand to avoid danger — is the specific tendency to avoid monitoring negative financial or performance information. While closely related to the broader concept of information avoidance, the ostrich effect refers specifically to the cyclical pattern of engagement and disengagement with quantitative information based on whether the news is expected to be good or bad. The term was coined by Galai and Sade (2006) in the context of financial markets, where they documented that investors systematically avoid checking portfolio values during market declines. Sicherman et al. (2016) confirmed this using data from Vanguard: logins to investment accounts dropped by 8-10% on days when the market fell significantly, and the effect was strongest among investors with the largest positions — those who had the most to learn from monitoring.

The peak–end rule holds that retrospective evaluations overweight an episode’s most intense moment and its ending while largely neglecting duration and average moment-to-moment quality. Mechanistically, episodic memory compresses continuous streams into a few diagnostic markers: affectively extreme peaks attract encoding, and recency makes the end highly retrievable. These summary memories guide subsequent judgments and choices more than the integral of experienced utility.

The placebo effect arises when expectations and learned associations engage top-down control that modulates perception and physiology, allowing an inert treatment to produce genuine symptom relief. Mechanistically, prefrontal and cingulate circuits influence pain and autonomic pathways via endogenous opioids, dopamine, and endocannabinoids, implementing predictive processing of treatment cues. Contextual signals—provider warmth, branding, price, and ritual—shape priors and reduce prediction error, which is experienced as improvement.

Pro-innovation bias is a cognitive and institutional tendency to overweight the prospective benefits of new technologies while underweighting costs, risks, externalities, and the adequacy of incumbent solutions. The mechanism operates through selective attention to promised gains, weak counterfactual baselines, and incentives that reward launch and adoption more than rigorous evaluation. It often presumes rapid, universal diffusion and frames resistance as irrational rather than as information about context and fit. The result is systematic overadoption or premature scaling.

The pseudocertainty effect is the tendency to treat an outcome as certain when certainty applies only within one stage of a multi-stage decision, while the overall outcome remains uncertain. The mechanism is stagewise, segregated evaluation: people mentally bank the guaranteed intermediate result and stop compounding probabilities across stages (the isolation effect in Prospect Theory). As a result, residual risk is underweighted and options that promise certainty at one node are favored over objectively equivalent single-stage options.

The recency illusion is a cognitive bias in which we mistake a shift in our own attention for a shift in the world, concluding that something is new or more prevalent simply because we have just started to notice it. The mechanism is attentional retuning: once a category becomes salient, subsequent instances are preferentially detected and encoded, inflating perceived frequency. This subjective sampling change is then misattributed to an objective base-rate change.

Self-selection bias arises when participation is non-random and driven by traits that also affect the outcomes of interest. Because motivation, time availability, dissatisfaction, or health status influence who opts in, the resulting sample systematically differs from the target population. The mechanism induces biased estimates: the participation decision is correlated with the variables being measured, undermining external validity unless strong assumptions hold.

Social proof—a term popularized by Robert Cialdini in his 1984 book 'Influence'—is the psychological tendency to look to other people's behavior as a guide for our own, particularly in situations of uncertainty or ambiguity. When we are unsure what to do, we assume that those around us possess more knowledge about the correct course of action. Social proof operates through multiple channels: expert endorsement, peer behavior, crowd size, user ratings, and testimonials. While it often serves as an efficient heuristic (following the crowd is frequently adaptive), it can also lead to herd behavior, information cascades, and the perpetuation of errors when the 'crowd' itself is misinformed.

The status quo effect, demonstrated in landmark research by William Samuelson and Richard Zeckhauser (1988), is the disproportionate preference for the current state of affairs simply because it is the current state. Even when objectively superior alternatives are available and switching costs are negligible, people tend to stick with what they already have. The effect is driven by multiple psychological mechanisms: loss aversion (changes involve potential losses that loom larger than equivalent gains), mere exposure (familiarity breeds preference), ambiguity aversion (known situations feel safer than unknown ones), and cognitive laziness (evaluating alternatives requires effort).

Subjective validation is the cognitive tendency to perceive a statement, prediction, or piece of information as accurate and meaningful primarily because it feels personally relevant—regardless of its objective truth value. The mechanism works because our brains are pattern-matching engines: when we encounter a description that seems to 'fit' our self-concept, we experience an emotional click of recognition that we mistake for evidence. This is why vague, universally applicable statements ('You sometimes doubt yourself but project confidence to others') feel uncannily precise. Subjective validation is the engine behind the Forer/Barnum effect and a cornerstone of pseudoscience, cold reading, and algorithmic personalization.

The sunk cost fallacy is the tendency to continue an endeavor because of past investments of time, money, or effort, even when future costs outweigh expected benefits.

System justification, a theory developed by John Jost and Mahzarin Banaji (1994), is the psychological tendency to defend, bolster, and legitimize existing social, economic, and political arrangements—even when those systems disadvantage the individual doing the defending. The theory proposes that people have a fundamental need to perceive the world as fair, orderly, and legitimate. When confronted with evidence of systemic inequality, this need can motivate people to rationalize the status quo rather than challenge it, because acknowledging unfairness threatens their sense of predictability and control. Paradoxically, research shows that members of disadvantaged groups sometimes exhibit stronger system-justifying beliefs than members of advantaged groups.

The time-saving bias, identified by Ola Svenson (2008), is a systematic error in how people estimate the time saved by increasing speed. Because the relationship between speed and travel time is hyperbolic (not linear), people dramatically overestimate time savings when accelerating at high speeds and underestimate savings when accelerating at low speeds. Intuitively, increasing speed from 30 to 40 km/h feels like a modest improvement, while increasing from 100 to 110 km/h feels significant—but mathematically, the former saves far more time per kilometer. This bias reflects a broader difficulty humans have with non-linear functions, similar to the challenges we face with compound interest, exponential growth, and probability.

Trait negativity bias is the specific tendency to weight negative personality traits far more heavily than positive ones when forming impressions of other people. A single perceived flaw — dishonesty, rudeness, unreliability — can overwhelm multiple positive qualities in our overall assessment, creating an asymmetry where negative information has disproportionate influence on person perception. Solomon Asch demonstrated this asymmetry as early as 1946: adding the single word 'cold' to an otherwise positive trait list (intelligent, skillful, industrious, determined, practical, cautious) dramatically altered participants' overall impressions, while adding 'warm' to a negative list had a much smaller positive effect. Baumeister, Bratslavsky, Finkenauer, and Vohs (2001) documented this pattern across domains in their landmark review 'Bad Is Stronger Than Good,' concluding that negative information is processed more thoroughly, remembered more accurately, and weighted more heavily in evaluations across virtually all psychological domains.

The value–action gap (also called the intention–behavior gap or attitude–behavior gap) is the pervasive and well-documented disconnect between what people say they value and how they actually behave. People genuinely hold values — environmental sustainability, healthy living, financial responsibility — yet systematically fail to act on them. This is not hypocrisy in the traditional sense; it reflects the fundamental tension between the deliberative cognitive system (which forms values and intentions) and the automatic behavioral system (which executes actions under the influence of habits, emotions, social pressure, and situational friction). Sheeran and Webb's (2016) meta-analysis of 422 studies found that a 'medium-to-large' change in intention produces only a 'small-to-medium' change in behavior — confirming that intentions are a necessary but grossly insufficient predictor of action. Icek Ajzen's Theory of Planned Behavior identifies perceived behavioral control as a key moderator: even strong intentions fail when people lack the perceived ability, opportunity, or resources to act.

Zero-sum bias is the cognitive tendency to intuitively perceive situations as zero-sum — where one party's gain must come at another party's expense — even when the situation objectively allows for mutual gains or mutual losses. The bias treats the 'pie' as fixed in size, ignoring the possibility that the pie can grow (positive-sum) or shrink (negative-sum) depending on the parties' actions. Rozycka-Tran, Boski, and Wojciszke (2015) developed the Belief in a Zero-Sum Game (BZSG) scale and found significant variation across cultures: societies with higher BZSG scores showed lower levels of interpersonal trust, social capital, and life satisfaction. The bias has deep evolutionary roots — in ancestral environments of genuine resource scarcity, zero-sum thinking was often accurate. In modern economies characterized by innovation, trade, and value creation, it is systematically misleading.

The fundamental attribution error is the tendency to explain other people's behavior in terms of personality and character while explaining our own behavior in terms of the situation. When a colleague misses a deadline, we think 'she's careless.' When we miss a deadline, we think 'I had too much on my plate.' We see others' actions as expressions of who they are, and our own as responses to what happened.

The actor–observer bias is the asymmetric way we explain behavior: When we are the actor, we weight the situation. When we are the observer, we weight the personality. Same action, two very different explanations depending on where we stand.

Illusory correlation is the tendency to see relationships between two variables that are actually unrelated – or to exaggerate a weak relationship. We remember the cases that confirm the pattern and forget the ones that contradict it, ending up with a 'rule' that has no basis in data.

The conjunction fallacy occurs when we believe a specific combination of events (A and B) is more likely than one of them alone (A). Mathematically this is impossible: the probability of A and B can never exceed the probability of A. But because the specific story feels more 'plausible,' intuition ranks it higher.

The spotlight effect is the tendency to overestimate how much others notice our appearance, mistakes, or behavior. We feel like we're standing under a spotlight, while everyone else is actually preoccupied with their own spotlight.

The illusion of transparency is the exaggerated belief that others can read our inner states – nervousness, dishonesty, attraction, boredom – on the outside of us. Because we feel the state so clearly ourselves, we assume it's equally visible to the observer.

The frequency illusion (also called the Baader–Meinhof phenomenon) is the experience that something you just learned about suddenly appears everywhere. The word, the car model, or the diagnosis has actually been just as common all along – but now you notice it.

Mental accounting is the tendency to treat money differently depending on which 'account' it mentally belongs to – salary, gift, bonus, tax refund, gambling winnings – even though every dollar is economically identical and fungible. A dollar is a dollar, but the brain treats them as if some had color and others shape.

Out-group homogeneity is the tendency to perceive members of 'other' groups as more similar to each other than members of one's own group. We see the diversity of the in-group in detail, while the out-group appears as a uniform mass – 'they're all like that.'

The group attribution error is the tendency to (a) assume that an individual group member's behavior reflects the whole group's preferences, or (b) assume that group decisions reflect each individual's views. We hop between individual and collective without accounting for the fact that groups and individuals aren't identical.

Rosy retrospection is the tendency to remember the past as better than it actually was. The details that were boring, exhausting, or frustrating fade, while the peaks and emotionally charged moments remain. The vacation was 'amazing,' even though during the trip we argued, got sick, and regretted the hotel.

The telescoping effect is the tendency to misplace past events in time: important recent events feel further back than they are (backward telescoping), while old but significant events feel closer than they are (forward telescoping). Memory stretches or shrinks the timeline according to emotional weight.

Declinism is the persistent belief that society, culture, or the world is in general decline – that 'everything was better before.' The conviction holds up regardless of what objective data show about health, life expectancy, poverty, education, or crime.

False memories are recollections of events that never happened, or substantial distortions of events that did. They feel subjectively as 'real' as true memories – often more vivid – and can be held with confidence even when objective documentation contradicts them.

The misinformation effect is the tendency for post-event information to alter what we remember about the event itself. After we've experienced something, questions, media coverage, or conversations can 'overwrite' the original memory without our noticing.

The ultimate attribution error is the tendency to explain negative behavior by out-group members as reflecting their character, while positive behavior is explained away as situational or exceptional. For our in-group the logic reverses: good deeds reflect character, bad ones are excused by circumstance.

The cross-race effect is the tendency to recognize and distinguish faces from one's own ethnic group more easily than faces from other groups. 'They all look alike' isn't conscious prejudice – it's a perceptual phenomenon stemming from which faces the brain has had most exposure to.

The cheerleader effect is the tendency for people to be judged more attractive when seen in a group than when seen alone. The group 'averages out' individual quirks, and the brain latches onto the average face – which is typically perceived as more attractive than most individual faces.

Not-invented-here (NIH) syndrome is the tendency to reject external ideas, products, or solutions in favor of internal ones, even when the external alternative is objectively better. The source weighs more heavily than the quality.

Reactive devaluation is the tendency to devalue a proposal solely because it comes from an opposing party. The exact same proposal feels better when it comes from an ally and worse when it comes from an opponent.

Suggestibility is the tendency to incorporate ideas, details, or interpretations from others into one's own memories and beliefs without noticing they came from an external source. Especially vulnerable are children, people under stress, and situations with authoritative senders.

Cryptomnesia is when a forgotten memory resurfaces but feels like a new, original thought. We 'invent' something we've previously heard, read, or seen – without realizing the source is external.

Fading affect bias (FAB) is the tendency for negative feelings attached to a memory to fade faster than positive ones. Over time we remember the good times as good, while the bad ones gradually lose their emotional edge.

The spacing effect is that learning sticks better when repetitions are spread out over time than when the same repetitions are packed into a single session. The same number of minutes yields substantially more durable memory when distributed across days.

The Von Restorff effect (also called the isolation effect) is the tendency for an item that stands out from its surroundings to be remembered better than the rest. What breaks the pattern sticks.

The picture superiority effect is the tendency to remember pictures better than words. After a day, people typically remember about 10% of what they've heard, but up to 65% when the information is paired with an image.

The continued influence effect is that misinformation keeps influencing thinking and decisions even after it has been clearly corrected. You can know something is false and still use it as a premise.

The Semmelweis reflex is the reflexive rejection of new findings, evidence, or ideas that contradict established norms or assumptions – without the evidence actually being evaluated on its own merits.

Selective perception is the tendency for expectations, interests, or identity to shape what we notice and how we interpret it – often without us being aware that the filtering is happening.

Choice-supportive bias is the tendency to remember the choice we made as better – and the alternatives we rejected as worse – than they actually were. Retrospective evaluation skews in favor of what we've already decided.

Post-purchase rationalization is the tendency to convince ourselves that a purchase – especially an expensive or impulsive one – was wiser than it actually was. Once the money is spent, the brain works to make the choice good.

The observer-expectancy effect occurs when a researcher or observer – unconsciously – influences the outcome of what they observe because they expect a particular result. The expectation seeps into interpretation, measurement, and subtle cues to participants.

Congruence bias is the tendency to test a hypothesis only by looking for observations that would confirm it – without checking whether alternative hypotheses fit at least as well. You test 'does it work?' instead of 'what would distinguish this from the alternative?'

Money illusion is the tendency to think about money in nominal amounts rather than real purchasing power. A 3% raise in a year with 5% inflation *feels* like a gain, even though you've actually lost purchasing power.

The subadditivity effect is the tendency to judge the probability of a whole as lower than the sum of the probabilities of the parts it consists of. Breaking an event into explicit sub-events makes the total feel more likely.

The less-is-better effect is the tendency to prefer a smaller option when it's evaluated on its own – but to prefer the larger one when both are compared side by side. The context of evaluation – not objective value – drives the choice.

The bike-shedding effect – also known as Parkinson's Law of Triviality – is the tendency to spend disproportionate time and attention on trivial questions, while large and complex decisions slip through with minimal discussion.

The rhyme-as-reason effect is the tendency to perceive statements that rhyme as more true than non-rhyming statements with the same content. Form influences judgment of content, without us being aware of it.

Restraint bias is the tendency to overestimate our own ability to resist temptation, impulse, and craving. We believe we can control ourselves in situations we're not currently in – and underestimate how much the temptation will pull on us once we're actually there.