Ux psychology skill

UX Psychology Principles

Overview

21 evidence-based psychology principles for building interfaces, plus Nielsen's 10 heuristics as an audit layer. Each principle in reference.md has a rule, its psychological mechanism, concrete implementation moves, and guardrails separating the honest version from the dark-pattern version.

Priority order when principles conflict: usability > honesty > persuasion. A persuasion pattern never justifies breaking a usability rule or a trust rule. Usability laws are load-bearing; persuasion is decoration on top.

How to Use

1. Before designing: scan the Quick Reference below, then read the matching numbered sections in reference.md for mechanism + implementation + guardrails of every principle you apply.
2. While building: apply interaction/perception laws (7–21) first; layer persuasion (1–6, trust) on top.
3. Before declaring any screen done: run the Review Checklist at the bottom of this file. It is the gate.

Quick Reference

Persuasion & motivation (reference Part I)

#	Principle	Rule
1	Smart Defaults	Pre-select the sensible choice for every field; never default anything costing money, data, or consent
2	Goal Gradient	Never start progress at 0% — count what the user already did; ≤7 visible steps; at the end, flip to "1 step left"
3	Reciprocity	Deliver standalone value before any signup gate; never blur/lock results the user generated — gate depth (export, history, hi-res), not the artifact
4	IKEA / Endowment	Let users build before the account wall; button says "Continue"/"Save", never "Sign up"; persist pre-signup work through account creation
5	Loss Aversion	Frame the concrete, personal, true cost of inaction; no fake urgency, no confirm-shaming
6	Anchoring	Never show a price in isolation; control the reference point (tier anchor, % of related purchase, monthly-equivalent); real anchors only

Interaction laws (reference Part II)

#	Principle	Rule
7	Fitts's Law	Primary actions big (≥44px) and near attention; destructive actions distant, never adjacent twins of Confirm
8	Hick's Law	Limit choices per screen; progressive disclosure; highlight one recommended option
9	Jakob's Law	Follow platform conventions; innovate on value, not controls
10	Miller / Chunking	Group in 3–5; never require remembering info across screens
11	Tesler's Law	Absorb complexity in code (auto-detect, parse, infer) — never push it to the user
12	Doherty Threshold	Acknowledge every interaction <400ms; manage perceived speed beyond that
13	Postel's Law	Accept any plausible input format and normalize silently; output precise and consistent
14	Pareto	Prime placement and polish for the critical 20% of features

Perception & memory (reference Part III)

#	Principle	Rule
15	Gestalt	Visual grouping must match logical grouping; labels closer to their own field than the neighbor's
16	Von Restorff	Exactly one visually distinct element per screen
17	Serial Position	Most important items first and last in any sequence
18	Peak-End	Engineer one peak moment; polish every ending — confirmations, errors, cancellation
19	Zeigarnik	Visible unfinished states pull users back — only for things they actually started
20	Aesthetic–Usability	Polish buys tolerance and trust, but masks problems in testing — measure task completion, not opinions
21	Banner Blindness	Critical info must never look like an ad or sit in banner/sidebar/carousel-shaped containers

Also in reference.md: Nielsen's 10 heuristics (Part IV), perceived performance — skeletons, optimistic UI, labor illusion (Part V), forms & microcopy — outcome-stating buttons, inline validation, never blame the user (Part VI), trust & social proof (Part VII), cross-cutting principles.

Common Mistakes

• Blurring the user's own generated result behind a signup modal. Feels like persuasion; reads as extortion. Show the real result, gate the depth (#3).
• Onboarding progress at "Step 1 of N" with nothing pre-filled. Count signup/input already given as completed progress (#2).
• Pre-signup work lost at the account wall. Persist state (localStorage → migrate on account creation); losing their work is the pattern's worst failure mode (#4).
• Animation-heavy specs with no accessibility notes. Shimmer, staggered reveals, and countdowns must respect reduced-motion, keyboard, screen readers, and ≥4.5:1 contrast. Accessibility is a floor, not a feature.
• Persuasion patterns on top of a confusing flow. Perfect anchoring on a broken checkout still loses; fix usability first.

Review Checklist (the gate)

Persuasion & motivation

• Every form field with a knowable answer has a smart, honest default
• Onboarding progress never starts at 0%; total visible steps ≤ 7
• User receives standalone value before any signup/email gate
• Users can build/customize something before the account wall; pre-signup state persists through signup
• Action prompts name a concrete, true cost of inaction; no confirm-shaming, no fake urgency
• No price appears without a controlled, honest reference point
• Social proof is real, specific, and recent
• Every persuasion pattern passes the test: "Is the underlying claim true?"

Interaction & layout

• Primary actions are big, close, and singular; destructive actions are distant and confirmed or undoable
• Choices per screen are limited; complexity is progressively disclosed, not dumped
• Navigation, icons, and flows follow platform conventions
• Content is chunked in groups of 3–5; nothing must be remembered across screens
• Complexity the code can absorb (formats, parsing, inference) never reaches the user
• Exactly one visually dominant element per screen; visual grouping matches logical grouping
• Important info never looks like an ad

Feedback & performance

• Every interaction acknowledges within ~400ms; longer work shows skeleton/progress/optimistic state
• Skeletons mirror real layout; optimistic updates have a rollback state
• Waits over ~5s explain what's happening
• Undo exists for reversible actions; confirmations reserved for irreversible ones

Forms, errors & copy

• Only necessary fields; inline validation on blur; input never lost on error
• Errors say what happened and the specific fix, in human language, next to the field
• Buttons state outcomes, not verbs ("Show 12 results," not "Submit")
• Anxiety-answering microcopy sits next to every commitment point

Final audit

• Screen passes Nielsen's 10 heuristics (reference.md Part IV)
• Works with keyboard, screen reader, and reduced motion; contrast passes WCAG AA