How people actually behave.

Anchoring

The first number a person sees pulls every number they estimate after it.

Also: Anchoring and adjustment

Loss aversion

Giving something up feels heavier than gaining the same thing felt good.

Framing effect

Describe the same outcome as a survival rate or a death rate and choices flip.

Sunk cost fallacy

Money and effort already spent keep people going long after the case has gone.

Also: Escalation of commitment

Availability heuristic

People judge how likely something is by how easily an example comes to mind.

Representativeness heuristic

People judge probability by resemblance to a stereotype, not by frequency.

Confirmation bias

People look for evidence that fits the belief they already hold.

Status quo bias

People stick with the current option, and defaults become the current option.

Decoy effect

Adding a clearly worse third option can shift which of the first two people pick.

Also: Asymmetric dominance

Hyperbolic discounting

Rewards lose value fast at first, so today beats tomorrow and preferences reverse.

Also: Present bias

Ambiguity aversion

People prefer a known risk to an unknown one, even at a worse expected value.

Also: Uncertainty aversion

Choice overload

Too many options can lower the chance someone chooses at all, under specific conditions.

Also: Paradox of choice

Compromise effect

An option gains share simply by sitting in the middle of the range offered.

Also: Extremeness aversion

Mental accounting

People sort money into separate mental buckets and refuse to move it between them.

Planning fallacy

People predict their own projects will finish sooner than similar projects ever have.

Optimism bias

People expect good things to happen to them more than to comparable others.

Also: Unrealistic optimism

Overconfidence effect

Confidence outruns accuracy, and confidence intervals come out far too narrow.

Base rate neglect

Given a vivid specific case, people forget how rare the category is.

Zero price effect

Free is not just a low price. Demand jumps discontinuously at zero.

Endowment effect

Owning something raises what you would sell it for above what you would pay.

Peak-end rule

People judge a past experience by its most intense moment and its final moment.

Also: Remembered utility

Serial position effect

Items at the start and end of a list are recalled better than items in the middle.

Also: Primacy and recency

Von Restorff effect

An item that differs from its neighbours is remembered better than the ones that match.

Also: Isolation effect

Zeigarnik effect

Unfinished tasks are said to stay in mind more readily than finished ones.

Also: Interrupted task effect

Picture superiority effect

Pictures are remembered better than the words that name them, especially over long delays.

Chunking

Grouping items into meaningful units lets working memory hold more of the same material.

Spacing effect

Study spread over time produces more durable memory than the same study massed together.

Also: Distributed practice

Testing effect

Retrieving something from memory strengthens it more than reading it again.

Also: Retrieval practice

Generation effect

Material a person produces themselves is remembered better than the same material read.

Recognition over recall

People identify the right option from a list far more reliably than they retrieve it from memory.

Hick's law

Choice reaction time grows with the logarithm of the number of equally likely alternatives.

Also: Hick-Hyman law

Fitts's law

Time to hit a target grows with distance and shrinks with target size.

Miller's law

Working memory holds a small number of chunks, closer to four than to seven.

Also: The magical number seven

Cognitive load

Working memory has a small budget, and interface noise spends it before the task does.

Change blindness

People miss large changes to a scene when the change coincides with a visual disruption.

Inattentional blindness

An unexpected object in plain view goes unseen when attention is committed elsewhere.

Banner blindness

People learn to ignore regions and shapes that historically carried advertising.

Attention residue

Part of attention stays on the previous task after switching, and degrades the next one.

Jakob's law

People spend most of their time on other products, so they expect yours to behave like those.

The gulf of execution and evaluation

Two gaps: working out how to act, and working out what happened after acting.

Also: Norman's gulfs

Goal gradient effect

Effort rises as the finish line gets closer, so the last steps are the cheapest to win.

Also: Gradient of reinforcement

Endowed progress effect

Give people a head start on a goal and more of them finish it.

Variable reward

Unpredictable payoffs hold behaviour longer than reliable ones, and resist stopping.

Also: Intermittent reinforcement

Operant conditioning and reinforcement schedules

Consequences shape behaviour, and the timing pattern of those consequences shapes it more than their size.

Also: Instrumental conditioning

Self-determination theory

People sustain effort when a task feels chosen, achievable and connected to others.

Also: SDT

Flow

Absorbed engagement appears when challenge matches skill and feedback is immediate.

Also: Optimal experience

The Fogg behaviour model

A behaviour happens when motivation, ability and a prompt land at the same moment.

Also: B = MAP

Implementation intentions

Naming when, where and how to act closes the gap between intending and doing.

Also: If-then plans

The habit loop

Repeated behaviour in a stable context becomes automatic and stops needing a decision.

Also: Cue, routine, reward

Commitment devices

People bind their future selves in advance because they expect to weaken later.

Also: Pre-commitment

Temptation bundling

Pair something you should do with something you want, and the should-do happens more.

The fresh start effect

Temporal landmarks make people feel disconnected from past failures and willing to try again.

The IKEA effect

People value what they built themselves above what the same thing is objectively worth.

Effort justification

Having paid a high price for something, people raise their opinion of it to match.

The progress principle

Visible progress in meaningful work is the strongest daily driver of engagement.

Streaks

A run of consecutive days becomes something to protect, which is the point and the problem.

Also: Chains

Overjustification effect

Paying people for something they already enjoyed can make them enjoy it less.

Also: Undermining effect

Gamification and its failure modes

Points, badges and leaderboards lift short-term activity and rarely change what people care about.

Also: Pointsification

Autonomy and reactance

Threaten someone's freedom to choose and they want the forbidden option more.

Also: Psychological reactance

Competence and mastery

People persist at things they believe they are getting better at.

Also: Self-efficacy

Social Proof

When people are unsure what to do, they copy what similar people already did.

Also: Informational social influence

Authority

People defer to signals of expertise and rank, often without checking the substance behind them.

Also: Expertise cue

Reciprocity

A gift creates a felt debt, and people repay it even when nobody asked them to.

Liking

People say yes more readily to sources they like, and similarity is the fastest route to liking.

Also: Affinity

Scarcity

Things feel more valuable when they look limited, and limits imposed by demand feel strongest.

Commitment and Consistency

A small public act creates pressure to keep behaving like the person who made it.

Also: Foot in the door

Descriptive versus Injunctive Norms

What people do and what people approve of are different messages, and mixing them up backfires.

Also: Norm boomerang

The Bandwagon Effect

Visible popularity creates more popularity, so early leads compound into outcomes nobody could predict.

Also: Cumulative advantage

In-group Favouritism

People favour their own group even when the group was assigned at random moments ago.

Also: Minimal group effect

Social Facilitation

Being watched sharpens easy tasks and degrades hard ones.

Also: Audience effect

Diffusion of Responsibility

The more people who could act, the less any single person feels they must.

Also: Bystander effect

The Benjamin Franklin Effect

Doing someone a favour can make you like them more, reversing the usual direction.

Reputation and Rating Systems

Ratings only discipline behaviour when raters are honest, and most designs quietly make them dishonest.

Identity Signalling

People choose products that say something about who they are, and avoid ones that say the wrong thing.

Also: Conspicuous consumption

Fear of Missing Out

Anxiety that others are having rewarding experiences you are absent from drives compulsive checking.

Also: FOMO

Conformity

People will endorse an obviously wrong answer rather than stand alone against a unanimous group.

Also: Asch conformity

The Spotlight Effect

People overestimate how much others notice and remember their appearance and mistakes.

Social Comparison

People judge their own ability and standing against others, especially when no objective measure exists.

Network Effects as Felt Experience

A network feels worthless until the specific people you care about are on it, then it feels essential.

Parasocial Relationships

Audiences form real felt bonds with people who do not know they exist.

Also: One-sided intimacy

The affect heuristic

People read a quick good or bad feeling off a thing and reason backwards from it.

Also: Feeling as information

Negativity bias

Bad events hit harder, stick longer and shape memory more than good ones of equal size.

Also: Bad is stronger than good

Hedonic adaptation

Emotional reactions to a changed situation fade as it becomes the new normal.

Also: The hedonic treadmill

Regret aversion

People choose to avoid the feeling of having chosen wrongly, not only to avoid the loss.

Anticipation and savouring

Waiting for something good can carry real pleasure, sometimes more than the thing itself.

The aesthetic-usability effect

People rate attractive interfaces as easier to use, sometimes regardless of actual ease.

The halo effect

One strong impression spreads to unrelated judgements about the same thing.

Mere exposure

Repeated exposure to something increases liking for it, with no reason required.

Also: The familiarity effect

Cognitive dissonance

Holding a belief and a conflicting action feels bad, so one of them bends.

Emotional design

Norman splits emotional response into gut reaction, use over time, and the story afterwards.

Also: Visceral, behavioural and reflective levels

Trust formation

Trust is judged fast on surface cues, then revised slowly by behaviour over time.

Perceived control and agency

Believing you can influence what happens reduces stress, even when you never act.

Uncertainty and anxiety

Not knowing what will happen is more stressful than knowing something bad will.

Privacy concern and the privacy paradox

Stated privacy concern and observed disclosure often diverge, and the framing is disputed.

Frustration thresholds and rage clicks

Frustration accumulates until a threshold, then behaviour turns abrupt and destructive.

Delight and its limits

Delight needs surprise to work, and surprise cannot be scheduled or repeated.

The service recovery paradox

A well-handled failure can leave people happier than no failure, but usually does not.

Psychological reactance to tone

Pressure on a free choice provokes resistance, and tone applies pressure as much as rules.

Waiting and perceived duration

How long a wait feels depends on occupation, explanation and certainty more than seconds.

Embarrassment and low-stakes failure

Fear of looking foolish stops people trying, even when nobody is watching.

Defaults

The preselected option wins far more often than the merits of the options explain.

Also: Default effect

Choice architecture

Every way of presenting options shapes the choice, and there is no neutral way.

Also: Decision architecture

Nudge theory

Small changes to how choices are presented can move behaviour without removing options.

Also: Libertarian paternalism

Friction as a design tool

Effort suppresses behaviour, which makes it a tool for slowing down the wrong actions.

Also: Design friction

Sludge

Friction that serves the institution and costs the user is sludge, not protection.

Also: Administrative burden

Salience

People weigh what they notice, and ignore true information that is not in front of them.

Also: Attention weighting

Partitioning

Dividing a resource into labelled parts creates natural stopping points and slows consumption.

Also: Earmarking

Pre-commitment

People will restrict their own future options when they expect their future self to waver.

Also: Commitment devices

Social norm messaging

Telling people what others actually do moves behaviour toward that number, in both directions.

Also: Descriptive norms

Feedback loops

Behaviour changes when its consequence returns quickly, specifically, and in a usable unit.

Also: Closing the loop

Simplification

Cutting steps, jargon and required inputs often beats persuasion by a wide margin.

Also: Burden reduction

Deadlines and time pressure

A real deadline converts vague intention into action; a fake one converts trust into churn.

Also: Scarcity framing

Reminders and prompts

Most intended actions fail at recall, so a well timed prompt outperforms more persuasion.

Also: Implementation intentions

Personalisation and its costs

Tailoring helps when it reduces work, and harms when it narrows what a person can see.

Also: Targeting

Transparency

Telling people how you are influencing them rarely stops the influence working.

Also: Disclosure

The dark pattern taxonomy

A named set of interface tricks that get users to do what they did not intend.

Also: Deceptive design

Confirmshaming

Wording the decline option to make the user feel foolish or mean for choosing it.

Also: Guilt decline

Forced continuity and roach motels

Easy to enter, hard to leave: the pattern that bills people for a decision they already reversed.

Also: Negative option billing

Debiasing techniques

Bias resists willpower, so the working fixes change the process rather than the person.

Also: Cognitive repairs

Ethical choice architecture

The line is whether the user would endorse the influence once it is explained to them.

Also: Nudge ethics