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Behavioral science · UX design
How people notice, decide, remember and act, turned into 50 rules you can check a screen against, from Hick's law and cognitive load to defaults and framing. Plus the 8 dark patterns that exploit the same psychology, so you can name them in a review.
By Sarit Elisha, founder of Irreplaceable · Updated October 10, 2026
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6 rules.
BEH-01
Every extra option slows the decision, and too many make people give up or pick at random. Group, recommend one, or hide advanced options.
Applies to: Screens that ask people to choose: plans, options, settings, menus.
BEH-02
Most people keep the default. A pre-ticked add-on, newsletter or data-sharing box is a choice made for them, and erodes trust when they notice.
Applies to: Pre-selected options, toggles and checkboxes.
BEH-03
A crossed-out price that was never charged, or a decoy plan that exists only to push another, is anchoring used against people; regulators treat fake reference prices as deceptive.
Applies to: Prices, plans and comparisons.
BEH-28
People stick with what they have even when the new option is better. Imports, defaults carried over and a clear 'what changes' lower the cost of moving.
Applies to: Migrations, new versions and switching from a competitor.
BEH-39
Smooth is not always good. A typed confirmation, a review step or a short delay before an irreversible action prevents the errors people regret most.
Applies to: Irreversible, costly or shared actions.
BEH-45
People click through confirmations on autopilot, so the dialog doesn't prevent the mistake. An undo after the fact actually does.
Applies to: Confirmation dialogs.
9 rules.
BEH-04
Working memory holds only a few things at once. Asking for everything on one screen raises errors and drop-off; split it, prefill it, or ask later.
Applies to: Forms, onboarding and dense screens.
BEH-05
Making people remember a code, a choice or a rule from an earlier step causes mistakes. Show it where it's needed.
Applies to: Anything people must remember from a previous screen.
BEH-06
Showing every detail up front buries the next step. Lead with what most people need and reveal the rest on demand.
Applies to: Settings, advanced features and long content.
BEH-20
People hold about four chunks at once. '4829 1173 0062' is read and checked; '482911730062' is mistyped.
Applies to: Long numbers, codes, IBANs, phone numbers and long lists.
BEH-21
People spend most of their time in other products and expect yours to work the same. A novel pattern costs learning on every first use.
Applies to: Icons, navigation, controls and their placement.
BEH-22
Some complexity can't be removed, only moved. Making people format a date, pick a timezone or know a code shifts the work and the errors to them.
Applies to: Inputs, formatting and setup.
BEH-30
People assume things that look alike work alike. A blue word that's a link in one place and a label in another breaks that, and they stop trusting the visual language.
Applies to: Repeated elements: links, buttons, tags, statuses.
BEH-36
The team knows what 'workspace', 'sync' or an acronym means; new users don't. Copy written from the inside leaves them guessing.
Applies to: Instructions, labels and empty states.
BEH-42
Easy-to-read text feels more true and trustworthy, and is understood by more people. Long, abstract or legalistic copy is skipped or misread.
Applies to: All copy.
9 rules.
BEH-07
People speed up as they see the end and abandon when they can't tell how far it is. Show steps or progress, and start it a little ahead if a step is already done.
Applies to: Multi-step flows, onboarding and profiles.
BEH-08
People judge an experience by its peak and its end. A flat or confusing ending colours the whole flow; confirm what happened and what comes next.
Applies to: Confirmation, success and end-of-flow screens.
BEH-09
A prompt works when people want to and can act now (Fogg model). Asking at the wrong moment trains them to dismiss it.
Applies to: Prompts to act: upgrades, invitations, reminders.
BEH-24
People remember unfinished tasks and want to close them. Showing what's left and where to pick up turns that pull into completion, instead of starting over.
Applies to: Long tasks, drafts and multi-step setup.
BEH-25
People who take a small step tend to continue. Asking for everything at once, before any commitment, loses most of them.
Applies to: Onboarding and big asks.
BEH-26
People give back after they receive. A sign-up or data request before they've seen any value feels like a toll and gets abandoned or faked.
Applies to: Sign-up walls, permission and data requests.
BEH-34
People overvalue now and discount later. 'Protect your account' loses to 'Skip'; showing what they get today, or making it one tap, gets it done.
Applies to: Security setup, backups, savings, health and other long-term actions.
BEH-43
People resist what they don't choose. A way to see why, adjust or turn off a recommendation keeps them using it; forcing it drives them away.
Applies to: Personalisation, recommendations and AI features.
BEH-44
People stay with what makes them feel capable. Specific, earned feedback on progress motivates; generic praise or constant streak pressure doesn't.
Applies to: Progress, achievements and feedback on skill.
3 rules.
BEH-10
'90% success' and '10% failure' feel different though they're the same. Loss-framed scare copy pushes decisions people later regret.
Applies to: Risks, fees, results and AI output.
BEH-11
'12 people are looking at this' that isn't true, or reviews from another product, is fake social proof and a recognised dark pattern.
Applies to: Reviews, counts of other users, badges.
BEH-37
Bad experiences weigh several times more than good ones. A harsh, blaming or alarming error colours the whole product; a calm one with a way forward doesn't.
Applies to: Errors, warnings and failure messages.
Designs that work against the person using them. Each one is a finding in a crit.
BEH-12
Countdown timers that reset and fake 'only 2 left' pressure people into choices; regulators in the EU, UK and US act against them.
Applies to: Timers, stock counts and limited offers.
BEH-13
Hiding cancel, or wording the decline button to shame ('No, I don't like saving money'), keeps people by friction and guilt, and costs trust and often legal exposure.
Applies to: Cancel, unsubscribe, decline and opt-out paths.
BEH-14
Fees revealed at the last step, items added to the basket, or a free trial that silently becomes paid exploit commitment and inattention.
Applies to: Checkouts, sign-ups and consent.
BEH-46
'You'll lose everything' to stop a cancellation exploits loss aversion and sunk cost. Say exactly what is kept, what goes and when.
Applies to: Cancellation, downgrade and deletion flows.
BEH-47
Asking again on every visit after someone declined wears them down rather than persuading them; it's a recognised dark pattern.
Applies to: Prompts, popups and upsells people already declined.
BEH-48
Ads made to look like content, or a button that does something other than it says, deceive people into actions they didn't choose.
Applies to: Ads, sponsored content and buttons.
BEH-49
Requiring an account, contacts or extra data to do something that doesn't need it, or defaulting to sharing more, takes what people didn't agree to give.
Applies to: Sign-ups, sharing and data collection.
BEH-50
'Uncheck this box if you don't want to not receive offers' is built to be misread, and consent obtained that way isn't consent.
Applies to: Opt-in and opt-out checkboxes and toggles.
1 rule.
BEH-15
Streaks and variable rewards build habits; aimed at engagement for its own sake they turn into compulsion and churn once people notice.
Applies to: Notifications, streaks and engagement loops.
5 rules.
BEH-16
People over-trust confident systems and stop checking. Show sources and uncertainty where a wrong answer costs something.
Applies to: AI suggestions, recommendations and automation.
BEH-27
People defer to authority cues. A badge, title or endorsement that isn't real or doesn't apply borrows trust it hasn't earned.
Applies to: Expert badges, certifications, 'recommended by'.
BEH-35
People underestimate time, and products do too. An estimate that's wrong by a lot breaks trust at the moment people are committing.
Applies to: Time and effort estimates: 'takes 2 minutes', step counts.
BEH-38
Seeing the steps being done makes waits feel worth it and raises trust. Fake steps or theatrical delays are deception that people eventually notice.
Applies to: Waits for search, AI answers and processing.
BEH-40
Asked at launch with no context, people refuse and rarely reconsider. Asked when the feature needs it, with what they get, most agree.
Applies to: Requests for location, camera, contacts, notifications and other permissions.
9 rules.
BEH-17
The time to hit a target grows with distance and shrinks with size. A main action tucked in a corner, or tiny and far from where the thumb or cursor is, slows every use.
Applies to: Primary and frequent actions.
BEH-18
People remember and notice what differs from its surroundings. When five things are highlighted, nothing is.
Applies to: Screens with one thing that matters most.
BEH-19
People remember and choose the first and last items best; the middle gets skipped. Bury the important option in the middle and it's missed.
Applies to: Lists, menus and navigation.
BEH-23
Responses under ~400 ms keep people in flow; slower ones need immediate acknowledgement, skeletons or optimistic updates, or people tap again and leave.
Applies to: Actions that take time: search, save, AI answers.
BEH-29
Flat text that's secretly a button gets missed; a card that looks clickable but isn't gets tapped in frustration.
Applies to: Buttons, links, cards and anything clickable or static.
BEH-31
People scan in F and Z patterns and read the first words of lines and headings. Front-load what matters; a heading that starts with 'In order to' hides it.
Applies to: Headings, list items and text people scan.
BEH-32
People ignore anything shaped and coloured like a banner. A real warning in an ad-like box is skipped.
Applies to: Important notices, warnings and offers.
BEH-33
People miss changes outside their focus. A total that updates at the top while they're at the bottom, or an error far from the field, goes unseen.
Applies to: Totals, errors and content that changes after an action.
BEH-41
Every badge competes for attention; when everything is urgent, people learn to ignore all of it, including what's important.
Applies to: Notifications, badges and red dots.
All the rules
The UX review checklist has every rule the crit checks: hierarchy, clarity, states, forms, AI behavior and RTL.