Glossary of thinking tools

This glossary defines all 130 thinking tools on ReadGlobe — 60 mental models, 60 cognitive biases, plus key ideas and schools of thought — each in one plain-English line, with a link to a full explainer.

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A

Action biasBias: The action bias is the tendency to favour doing something over doing nothing, even when action is no better — or worse — than waiting.
Activation energyMental model: Activation energy is the initial push required to start a reaction or change — the upfront cost of getting going, even when the change is beneficial once underway.
Actor–observer biasBias: The actor–observer bias is our tendency to attribute our own actions to the situation but other people’s actions to their character.
Affect heuristicBias: The affect heuristic is the mental shortcut of judging something — its risks, benefits, and merits — by the emotion it triggers rather than by analysis.
The Allegory of the CaveIdea: Plato's image of prisoners mistaking shadows on a wall for reality — a picture of how education turns the soul from illusion toward truth.
Amor FatiIdea: The Latin phrase "love of fate" — embracing everything that happens, including suffering, not merely tolerating it.
Analytical PsychologySchool: The school founded by Carl Jung that studies the unconscious through archetypes, the collective unconscious, and the process of individuation.
Anchoring biasBias: Anchoring bias is the tendency to rely too heavily on the first piece of information encountered — the “anchor” — when making decisions.
AntifragilityMental model: Antifragility is the property of things that gain from disorder — they grow stronger under stress, volatility, and shocks rather than merely resisting them.
Authority biasBias: Authority bias is the tendency to over-trust and obey an authority figure regardless of the content of what they say.
Availability cascadeBias: An availability cascade is a self-reinforcing cycle in which an idea gains plausibility through sheer repetition in public discourse.
Availability heuristicBias: The availability heuristic is judging how likely or frequent something is by how easily examples come to mind.

B

Backfire effectBias: The backfire effect is when being shown evidence that contradicts a deeply held belief makes you hold that belief even more strongly, rather than revising it.
Bandwagon effectBias: The bandwagon effect is the tendency to adopt beliefs or behaviours because many others already have.
Barbell strategyMental model: The barbell strategy is combining two extremes while avoiding the middle: pairing a very safe core with a small allocation of high-risk, high-upside bets.
Barnum effectBias: The Barnum effect is the tendency to accept vague, general personality descriptions as uniquely accurate about yourself.
Base-rate neglectBias: Base-rate neglect is the tendency to ignore how common or rare something is (the base rate) and judge by specific, vivid details instead.
Bayesian thinkingMental model: Bayesian thinking is updating your beliefs in proportion to new evidence — starting from a prior probability and revising it as data arrives, rather than holding fixed opinions.
Bias blind spotBias: The bias blind spot is the tendency to recognise cognitive biases in other people while failing to see them in yourself.
BottleneckMental model: A bottleneck is the single constraint that limits the output of an entire system — the narrowest point through which everything must pass.

C

The Categorical ImperativeIdea: Kant's supreme moral rule: act only on a principle you could will everyone to follow, and treat people as ends, never merely as means.
Chesterton's fenceMental model: Chesterton's fence is the principle that you should not remove or change something until you understand why it was put there in the first place.
Choice overloadBias: Choice overload is the finding that too many options can make us less likely to decide, less satisfied with what we pick, and more prone to regret.
Circle of competenceMental model: Your circle of competence is the set of areas where you genuinely have expertise.
Clustering illusionBias: The clustering illusion is the tendency to see patterns, streaks, or clusters in what is actually random data.
Cognitive dissonanceBias: Cognitive dissonance is the mental discomfort of holding two conflicting beliefs, or of acting against your beliefs.
Comparative advantageMental model: Comparative advantage is the principle that you should specialise in what you give up the least to produce, then trade — even if someone else is better at everything.
CompoundingMental model: Compounding is growth that feeds on itself: returns generate further returns, so gains accelerate over time rather than adding up linearly.
Confirmation biasBias: Confirmation bias is the tendency to seek, interpret, and remember information that confirms what you already believe, while discounting evidence that contradicts it — making beliefs feel better justified than the evidence actually warrants.
Contrast effectBias: The contrast effect is when our judgement of something shifts depending on what we compare it to.
Creative destructionMental model: Creative destruction is the process by which new innovations replace and dismantle the old — Joseph Schumpeter’s term for how capitalism continually revolutionises itself from within, destroying established companies and industries even as it creates new ones.
Critical massMental model: Critical mass is the threshold at which a system becomes self-sustaining — the point where enough has accumulated for a process to keep going on its own.
The curse of knowledgeBias: The curse of knowledge is the difficulty experts have imagining what it’s like not to know what they know.

D

The decoy effectBias: The decoy effect is when adding a third, deliberately inferior option changes which of the original two you prefer.
Diminishing returnsMental model: Diminishing returns is the principle that as you add more of one input, the extra output it produces eventually shrinks.
Dunbar's numberMental model: Dunbar's number is the theory that humans can maintain only about 150 stable social relationships — the cognitive limit on the number of people with whom you can sustain meaningful, reciprocal connections.
Dunning–Kruger effectBias: The Dunning–Kruger effect is the tendency for people with low competence in a domain to overestimate their ability — because the very skills needed to perform well are also the skills needed to recognize poor performance.

E

Economic moatMental model: An economic moat is a durable competitive advantage that protects a business from rivals, the way a moat protects a castle.
Economies of scaleMental model: Economies of scale are the cost advantages a business gains as it grows: producing more spreads fixed costs over more units, so the cost per unit falls.
EmergenceMental model: Emergence is when a system exhibits properties or behaviours that its individual parts do not have on their own.
Empathy gapBias: The empathy gap is the difficulty of understanding or predicting behaviour — your own or others’ — across different emotional or physical states.
Endowment effectBias: The endowment effect is the tendency to value something more highly simply because you own it.
EntropyMental model: Entropy is a measure of disorder, and physics says it always increases in a closed system.
ErgodicityMental model: Ergodicity is whether the average outcome across many people (the ensemble average) equals the average for one person over time (the time average).
Eternal RecurrenceIdea: Nietzsche's thought-experiment: if you had to live your life over and over, identically, forever — could you affirm it?
ExistentialismSchool: A philosophy holding that existence precedes essence — we are not born with a fixed purpose but must create meaning through our choices.
Expected valueMental model: Expected value is the average outcome of a decision if you could repeat it many times — each possible result weighted by its probability.

F

False-consensus effectBias: The false-consensus effect is the tendency to overestimate how much other people share your beliefs, values, and behaviours.
First-principles thinkingMental model: First-principles thinking is breaking a problem down to its most basic, undeniable truths and reasoning up from there — rather than reasoning by analogy to how things are usually done.
FlywheelMental model: A flywheel is a self-reinforcing loop where each part feeds the next, so momentum builds over time.
Framing effectBias: The framing effect is when the way information is presented — not its content — changes your decision.
Frequency illusionBias: The frequency illusion is the experience of noticing something everywhere right after you first encounter it — a word, a car model, an idea.
Fundamental attribution errorBias: The fundamental attribution error is the tendency to explain other people’s behaviour by their character but our own by circumstance.

G

The gambler’s fallacyBias: The gambler’s fallacy is the belief that past random events change the odds of future ones — that after a run of reds, black is "due." For independent events the probability resets every time; the coin has no memory.
Game theoryMental model: Game theory is the study of strategic decisions, where your best move depends on what others choose and theirs depends on you.
Goodhart's lawMental model: Goodhart's law states that when a measure becomes a target, it ceases to be a good measure.

H

Halo effectBias: The halo effect is letting one positive trait — often attractiveness, likability, or success in one area — color your overall judgement, so a good impression in one dimension spills over into unrelated ones you haven’t actually assessed.
Hanlon’s razorMental model: Hanlon’s razor says: never attribute to malice that which is adequately explained by stupidity, carelessness, or circumstance.
Hindsight biasBias: Hindsight bias is the tendency, after an event, to see it as having been predictable all along.
Hot-hand fallacyBias: The hot-hand fallacy is the belief that someone who has succeeded several times in a row is "on a streak" and more likely to succeed again — even when each attempt is statistically independent.
Hyperbolic discountingBias: Hyperbolic discounting is our tendency to prefer smaller rewards that arrive sooner over larger rewards that come later — and to do so far more steeply for near-term choices.

I

The IKEA effectBias: The IKEA effect is the tendency to place disproportionately high value on things we partly made ourselves.
Illusion of controlBias: The illusion of control is the tendency to overestimate how much influence you have over outcomes that are largely or entirely down to chance.
Illusion of transparencyBias: The illusion of transparency is the tendency to overestimate how well others can perceive your inner states — your nervousness, feelings, or thoughts.
Illusory correlationBias: Illusory correlation is perceiving a relationship between two things when none exists, or seeing one far stronger than it really is.
Illusory superiorityBias: Illusory superiority is the tendency to overestimate your qualities relative to others — to rate yourself above average on skill, ethics, and judgement.
In-group biasBias: In-group bias is the tendency to favour people we see as part of our group — and to be more critical or suspicious of outsiders.
IncentivesMental model: Incentives are the rewards and punishments that drive behaviour.
InversionMental model: Inversion is solving a problem from the opposite end — asking how to fail, then avoiding that.

J

Just-world hypothesisBias: The just-world hypothesis is the tendency to believe the world is fundamentally fair — that people get what they deserve and deserve what they get.

L

LeverageMental model: Leverage is using a small input to produce a disproportionately large output — Archimedes’ "give me a lever long enough and I will move the world." As a mental model, it asks where a little effort, capital, or insight can be amplified into outsized results.
The Lindy effectMental model: The Lindy effect says that for non-perishable things — ideas, books, technologies — life expectancy grows with age.
Local vs global optimumMental model: A local optimum is the best option within your immediate vicinity; a global optimum is the best option overall.
Loss aversionBias: Loss aversion is the tendency to feel the pain of a loss about twice as strongly as the pleasure of an equivalent gain.

M

The map is not the territoryMental model: “The map is not the territory” means any model, description, or belief is a simplified representation of reality — never reality itself.
Margin of safetyMental model: Margin of safety is building a buffer between what you expect and what you can withstand — so that errors, bad luck, or wrong assumptions don’t cause catastrophe.
Marginal thinkingMental model: Marginal thinking is making decisions based on the next additional unit — the extra cost and extra benefit of one more — rather than on totals or averages.
The mere-exposure effectBias: The mere-exposure effect is the tendency to like things simply because they’re familiar.
Metcalfe's lawMental model: Metcalfe's law states that the value of a network grows roughly with the square of the number of its users (n²), because each new user can connect with all the others.
Moore's lawMental model: Moore's law is the observation that the number of transistors on a chip roughly doubles every two years, so computing power grows exponentially while cost falls.
Mr. MarketMental model: Mr.

N

Nash equilibriumMental model: A Nash equilibrium is a state in a game where no player can do better by changing their strategy alone, given what everyone else is doing.
Natural selectionMental model: Natural selection is the process by which traits that aid survival and reproduction become more common over generations.
Negativity biasBias: Negativity bias is the tendency for negative events, emotions, and information to affect us more strongly than equally intense positive ones.
Network effectsMental model: A network effect is when a product or service becomes more valuable as more people use it.

O

Occam’s razorMental model: Occam’s razor is the principle that, among competing explanations, the one requiring the fewest assumptions is usually the best place to start.
Omission biasBias: The omission bias is the tendency to judge harmful actions as worse than equally harmful inactions.
Opportunity costMental model: Opportunity cost is the value of the best alternative you give up when you make a choice.
Optimism biasBias: Optimism bias is the tendency to overestimate the likelihood of good outcomes and underestimate the bad — believing you’re personally less at risk than others of negative events, from illness to project overruns.
OptionalityMental model: Optionality is having choices with limited downside and large potential upside — keeping options open so you can benefit from good outcomes while capping your losses on bad ones.
The ostrich effectBias: The ostrich effect is the tendency to avoid negative information — to "bury your head in the sand" rather than face something unpleasant.
Overconfidence effectBias: The overconfidence effect is the gap between how accurate people think their judgements are and how accurate they actually are.

P

The Pareto principleMental model: The Pareto principle — the 80/20 rule — observes that for many outcomes, roughly 80% of effects come from 20% of causes.
Parkinson's lawMental model: Parkinson's law is the observation that work expands to fill the time available for its completion.
Path dependenceMental model: Path dependence is when the outcomes available today are constrained by the sequence of decisions and events that came before — history matters, and early choices can lock in long after the reasons for them have vanished.
The peak-end ruleBias: The peak-end rule is the finding that we judge an experience largely by how it felt at its most intense moment (the peak) and at its end — not by the sum or average of the whole.
Pessimism biasBias: The pessimism bias is the tendency to overestimate the likelihood of negative outcomes and underestimate positive ones — expecting things to turn out worse than they statistically do.
The Peter principleMental model: The Peter principle states that in a hierarchy, people tend to rise to their level of incompetence.
The planning fallacyBias: The planning fallacy is the tendency to underestimate how long a task will take, how much it will cost, and how likely it is to go wrong — even when you know similar past tasks ran over.
Preferential attachmentMental model: Preferential attachment is the tendency for those who already have more to gain still more — "the rich get richer." In networks and society, new connections, attention, or resources flow disproportionately to whoever already has the most, widening the gap over time.
Primacy effectBias: The primacy effect is the tendency to remember and be most influenced by the first items in a sequence.
Prisoner's dilemmaMental model: The prisoner's dilemma is a game where two players each do better by betraying the other, so both betray and both end up worse than if they had cooperated.
Projection biasBias: The projection bias is the tendency to assume your future self will share your current preferences, emotions, and states.
Pygmalion effectBias: The Pygmalion effect is when higher expectations placed on someone lead to better performance — and lower expectations to worse.

R

ReactanceBias: Reactance is the urge to do the opposite of what you’re told when you feel your freedom of choice is being threatened.
Recency biasBias: Recency bias is the tendency to give the most recent events disproportionate weight in judgements and predictions — assuming what just happened will keep happening, while older but relevant information quietly fades from view.
Red Queen effectMental model: The Red Queen effect is the need to keep improving just to maintain your position, because competitors and the environment are improving too.
RedundancyMental model: Redundancy is having backup capacity — spare parts, reserves, multiple pathways — so that the failure of one component doesn’t bring down the whole system.
Regression to the meanMental model: Regression to the mean is the tendency for extreme results to be followed by more average ones, simply because luck evens out.
Representativeness heuristicBias: The representativeness heuristic is judging the probability of something by how closely it matches a mental prototype, rather than by actual statistics.

S

Second-order thinkingMental model: Second-order thinking is considering not just the immediate result of a decision but the consequences of those consequences — the “and then what?” effects that ripple out over time.
Self-serving biasBias: Self-serving bias is the tendency to take credit for successes but blame failures on outside forces.
The ShadowIdea: Jung's term for the disowned parts of the self — traits we deny and project onto others — which must be integrated to become whole.
Signal vs noiseMental model: The signal-to-noise model distinguishes meaningful information (signal) from random, irrelevant fluctuation (noise).
Skin in the gameMental model: Skin in the game means having a personal stake in an outcome — sharing in the losses, not just the gains.
The spotlight effectBias: The spotlight effect is the tendency to overestimate how much others notice and judge you.
Status-quo biasBias: Status-quo bias is the preference for things to stay the same — sticking with the current option or default simply because it’s the current one.
StoicismSchool: A Greco-Roman philosophy holding that virtue is the only true good and that we should focus only on what is within our control.
Streetlight effectMental model: The streetlight effect is searching for answers where it’s easiest to look rather than where the answer actually is.
Sunk-cost fallacyBias: The sunk-cost fallacy is continuing a course of action because of resources already invested — time, money, or effort — even when quitting would be the better choice.
Supply and demandMental model: Supply and demand is the model that prices and quantities are set by the interaction of how much sellers offer and how much buyers want.
Survivorship biasBias: Survivorship bias is focusing on the people or things that made it through a selection process while overlooking those that didn’t — usually because the failures are invisible.
Switching costsMental model: Switching costs are the time, money, effort, and risk a customer must spend to move from one product to a competitor.
Systems thinkingMental model: Systems thinking is understanding something by how its parts interact as a whole — through feedback loops, delays, and relationships — rather than analysing parts in isolation.

T

TaoismSchool: A Chinese philosophy of living in harmony with the Tao — the natural way of things — through simplicity, humility, and effortless action.
Tragedy of the commonsMental model: The tragedy of the commons is when individuals, each acting in their own rational self-interest, deplete a shared resource that everyone needs — because the benefit of overusing it is personal while the cost is spread across all.

V

Via negativaMental model: Via negativa is the principle that improvement often comes from removing the harmful, false, or unnecessary rather than adding something new.

W

Wu WeiIdea: The Taoist principle of "effortless action" — accomplishing things by aligning with the natural flow rather than forcing them.

Z

The Zeigarnik effectBias: The Zeigarnik effect is the tendency to remember unfinished or interrupted tasks better than completed ones.
Zero-sum vs positive-sumMental model: A zero-sum game is one where one person’s gain is another’s exact loss — the pie is fixed.

Every definition links to a full explainer with examples, mechanisms, and related concepts. Editorial synthesis © ReadGlobe 2026, drawing on the cognitive-science and mental-models literature.