THE PLAYBOOK

The behavioral principles behind great product design.

The mental shortcuts every product quietly relies on. Tap any principle to see the real teardowns that put it to work.

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Hick's Law

The more choices you present, the longer a decision takes.

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Confirmation Bias

We seek and favor evidence that supports what we already believe.

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Priming

Earlier exposure to a stimulus shapes later perception and choices.

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Cognitive Load

The total mental effort a task demands of working memory.

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Anchoring Bias

The first value encountered biases all the judgments that follow.

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Nudge

Small cues can steer behavior without restricting choice.

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Progressive Disclosure

Reveal complexity gradually so users are not overwhelmed up front.

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Fitts's Law

Bigger, closer targets are faster and easier to hit.

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Attentional Bias

Recurring thoughts shape what we notice in our surroundings.

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Empathy Gap

We underestimate how strongly emotions drive behavior.

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Visual Anchors

Design elements that guide where the eye travels.

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Von Restorff Effect

The item that stands out from its peers is the one remembered.

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Visual Hierarchy

The order in which the eye perceives elements on a screen.

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Selective Attention

When focused, we filter out the surrounding distractions.

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Survivorship Bias

We overlook the things that did not make it past a selection.

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Banner Blindness

Users learn to ignore elements they see repeatedly.

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Juxtaposition

Elements that are close and similar read as a single unit.

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Signifiers

Cues that communicate what an element will do.

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Contrast

Attention is drawn to elements with greater visual weight.

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External Trigger

Guidance for the next action sits inside the prompt itself.

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Decoy Effect

A deliberately weaker option makes another option look better.

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Centre-Stage Effect

People tend to pick the middle option in a set.

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Framing

How information is presented changes the decision people make.

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Law of Proximity

Elements placed close together are perceived as related.

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Tesler's Law

Complexity can be reduced but never removed — someone absorbs it.

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Spark Effect

People act more readily when the required effort is small.

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Feedback Loop

Acting and immediately seeing the result of that action.

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Expectations Bias

Our own expectations color what we perceive.

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Aesthetic-Usability Effect

Attractive designs are perceived as easier to use.

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Social Proof

We mirror the behavior of others, especially under uncertainty.

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Scarcity

Limited availability makes something feel more valuable.

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Curiosity Gap

A hint of missing information creates a pull to seek it out.

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Mental Model

Users arrive with assumptions about how things should work.

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Familiarity Bias

People prefer experiences that are already familiar.

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Halo Effect

One positive trait colors our judgment of the whole.

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Miller's Law

Working memory holds only about seven items at once.

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Unit Bias

One serving of something feels like the right amount.

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Flow State

Being fully immersed and focused in a task.

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Skeuomorphism

Real-world resemblance helps users grasp interfaces faster.

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Reciprocity

Receiving something creates an urge to give back.

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Singularity Effect

We care more about one identifiable person than a group.

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Authority Bias

We give more weight to the opinion of an authority figure.

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Pseudo-Set Framing

Framing tasks as a set makes finishing them more tempting.

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Variable Reward

Unpredictable rewards are especially compelling.

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Group Attractiveness Effect

Items look more attractive shown in a group than alone.

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Curse of Knowledge

Experts forget that others lack their level of context.

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Aha! Moment

The instant a new user first grasps your product's value.

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Self-Initiated Triggers

People respond more to prompts they set up for themselves.

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Survey Bias

People skew answers toward what feels socially acceptable.

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Cognitive Dissonance

Holding two conflicting ideas at once is uncomfortable.

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Goal Gradient Effect

Effort and motivation rise as the goal gets closer.

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Feedforward

Letting users know what to expect before they act.

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Occam's Razor

The simplest adequate solution is usually the best one.

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Noble Edge Effect

People favor socially responsible companies.

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Hawthorne Effect

People change their behavior when they know they are watched.

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Hindsight Bias

After the fact, outcomes feel like they were predictable.

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Law of Similarity

Similar-looking elements are perceived as related.

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Law of Prägnanz

We read ambiguous shapes in the simplest possible form.

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Streisand Effect

Trying to suppress information ends up spreading it.

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Spotlight Effect

We overestimate how much others notice us.

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Fresh Start Effect

A sense of new beginnings motivates people to act.

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Labor Illusion

Visible effort makes a result feel more valuable.

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Default Bias

People tend not to change an established behavior.

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Investment Loops

When users invest themselves, they are more likely to return.

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Loss Aversion

Avoiding a loss matters more than an equivalent gain.

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Commitment & Consistency

People stay consistent with their previous actions.

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Sunk Cost Effect

We stay invested in something because we already invested.

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Decision Fatigue

Many decisions erode the quality of the next ones.

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Reactance

People resist a behavior when they feel forced into it.

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Observer-Expectancy Effect

A researcher's bias can unconsciously sway participants.

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Weber's Law

People adapt more easily to small, incremental changes.

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Law of the Instrument

Over-relying on a familiar tool for every problem.

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Temptation Bundling

Pairing a chore with a treat makes it easier to start.

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Parkinson's Law

Work expands to fill the time allotted to it.

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Dunning-Kruger Effect

Low skill comes paired with overestimated confidence.

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Affect Heuristic

Our current emotions cloud and influence our judgment.

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Hyperbolic Discounting

We favor smaller immediate rewards over larger later ones.

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Chronoception

Our perception of time is subjective.

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Cashless Effect

People spend more when the money is not physically visible.

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Self-Serving Bias

We claim credit for wins and blame others for losses.

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Pareto Principle

Roughly 80% of effects come from 20% of causes.

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Discoverability

How easily users can discover your features.

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Backfire Effect

Challenging a belief can make it grow stronger.

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False Consensus Effect

We overestimate how much others agree with us.

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Bandwagon Effect

Adoption grows in proportion to those who already adopted.

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Second-Order Effect

The consequences of the consequences of our actions.

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Barnum-Forer Effect

Vague, generic descriptions feel personally accurate.

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IKEA Effect

We value things more when we partly created them ourselves.

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Planning Fallacy

We underestimate how long a task will take.

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Provide Exit Points

Invite users to leave the app at the right moment.

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Peak-End Rule

We judge an experience by its peak and how it ends.

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Sensory Appeal

Engaging multiple senses makes experiences more memorable.

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Zeigarnik Effect

Unfinished tasks are remembered better than completed ones.

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Endowment Effect

We value something more once it feels like ours.

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Chunking

Grouped information is easier to remember.

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Picture Superiority Effect

Pictures are remembered better than words.

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Method of Loci

We recall things better when tied to a location.

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Shaping

Reinforcing small steps toward a target behavior.

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Delighters

Unexpected, playful touches are remembered fondly.

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Internal Trigger

A memory or emotion prompts the next action.

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Recognition Over Recall

Recognizing something is easier than recalling it.

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Storytelling Effect

Stories are remembered better than facts alone.

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Negativity Bias

Negative events are recalled more than positive ones.

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Availability Heuristic

Recent, easily recalled information feels more important.

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Spacing Effect

Spaced-out study sessions beat cramming for retention.

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Serial Position Effect

The first and last items in a list are easiest to recall.