Week 39 · Human Interaction Psychology

Say “Law”
Prove It

Twelve principles got you through this quarter — Fitts, Hick, Jakob, colour, Gestalt, calm, micro-interactions, accessibility, dark patterns, aesthetic-usability, gamification, emotional design. Only some of them earned the word ‘law.’ One flawed checkout screen, coming up, is carrying six of their failures at once — before you are told which.

Predict

How many of this quarter's twelve laws are broken on the one checkout screen below?

The diagnostic

0/6 diagnosed

Void MarketCheckout

Field recorder, matte black

$214.00

Shipping method

Promo code

Gift card

Tap a numbered pin above. Every one of them is a real defect this checkout ships with.

Part I

Eight Screens, Ten Seconds Each

Recognising a law you already read about once is not the same skill as recognising it cold, under a clock, on a screen you have never seen.

Below are eight tiny interfaces, each carrying exactly one defect. Ten seconds a screen, pausable if you need to think without the clock running. Nothing here is scored against you — the only thing being measured is your own time, screen to screen, as the shape of a Fitts problem or a Jakob problem stops needing a re-read.

Screen 1 of 8

Start when ready

The trend line fitted at the end is the same regression logic Fitts and Hick used on their own subjects — movement time falling as a task gets practised is not a metaphor borrowed from this quarter, it is the exact mechanism Part 2 of the dossier grades ROBUST and SUPPORTED for two of these twelve laws specifically.

Part II

Design “Laws” Are Not Laws

Say “Fitts’s Law” and “Jakob’s Law” in the same sentence and you have implied they are the same kind of object. They are not.

One is a mathematical model fitted to reciprocal-tapping data, replicated and reformulated across seventy years of research, now embedded in an engineering standard. The other is a name Jakob Nielsen gave to a real pattern from his own usability-testing practice — useful, but never subjected to a controlled experiment with a measured effect. Both get called “laws.” Only one earned the word.

Predict

Which of these twelve carries the strongest evidence base — the closest thing on this list to an actual law of physics?

Four grades sort the twelve honestly. ROBUST — large, replicated experimental literature, a precise model, tested across contexts. SUPPORTED — genuine experimental basis, real replication, but a narrower base or contested boundary conditions. CONTESTED — mixed results, or a popular claim a meta-analysis has already complicated. HEURISTIC — a practitioner’s real, useful naming of a pattern, with no controlled experiment behind the name itself. None of the HEURISTIC entries are wrong to use — they are design vocabulary, not design law, and the difference matters the moment one of them is used to end a disagreement a five-user test could settle in a day.

Twelve laws, three families

Motor & Decision

Perceptual

Motivational

the constraint on all three

Group the twelve by what they actually govern and a shape appears. Motor & decision laws price the cost of reaching and choosing — Fitts prices the reach, Hick prices the choice, Jakob prices how much of that cost transfers from everywhere else you have ever tapped, and Calming UI prices the whole screen’s worth of attention before any single option is even chosen. Perceptuallaws price what the eye organises before a word is read — Gestalt’s grouping votes, colour’s contested emotional claims, and the aesthetic-usability halo that lets a beautiful screen borrow patience it has not earned. Motivational laws price what keeps someone coming back or leaving on command — micro-interactions’ feedback, gamification’s loops, emotional design’s tone, and dark patterns as the name for when any of the three above gets pointed at the business instead of the user. Accessibility sits underneath all three, not beside them — a constraint, not a competing family.

The word “law” in design writing buys nothing on its own.

Topic 39 dossier, The Quarter in One Paragraph

Part III

The Quarter, Week by Week

Twelve weeks, one at a time, in the order you actually met them.

Each stop below carries its own mental model, its own evidence grade, and its own week — the same takeaway that closed that week’s own essay, not a summary of it. Visit any of them; nothing here reimplements what that week already built.

Week

FittsEmotional Design

Fitts — Week 27

ROBUST

Whenever a user misses, hesitates, or says they ‘can’t find’ a control, look for the ratio of distance to width behind it, not their attention span — you control both sides of that ratio, and every halving or doubling costs exactly one measurable bit.

Visit Fitts's Law

Part IV

One Screen, Audited

The same checkout from the very top of this essay, put through the audit this whole quarter was training you to run.

Drag the divider. Six of the twelve laws changed something you can see. The other six were checked and held constant — named honestly below rather than left uncredited, because an audit that only shows its wins is not an audit.

Jakob's Law — Cart moved to the top-right corner every other store already trained the thumb to expect.
Dark Patterns — Warranty defaults off. Nothing is pre-selected against the user’s own subtotal.
Hick's Law — Twelve methods collapsed to one frequency-weighted default, the rest one tap away.
Calming UI / Progressive Disclosure — That collapse is deferral, not deletion — “11 more” stays honest about what is hidden.
Gestalt Grouping — Gift card field removed rather than left ambiguously close to promo code’s own label.
Color Psychology — Buy now now reads as confident and intentional; Remove item stopped shouting for an unremarkable action.
Fitts's Law — Place order is large and alone in reach; Cancel shrank and moved away — friction spent on purpose.
Universal Accessibility — Held constant, checked not shown here: every label is visible text, every target clears 44px, contrast clears AA.
Aesthetic–Usability Effect — The after screen also looks calmer — but the fixes above are what actually shortened the task, not the polish.
Micro-interactions — Held constant, checked not shown here: Place order gives an immediate, proportional confirmation on press.
Gamification — Held constant, checked not shown here: no streak, badge or reward loop was inserted into a purchase flow that never asked for one.
Emotional Design — Held constant, checked not shown here: confirmation copy stays warm, not jokey — real money just moved.

Part V

Law Collisions

No interface obeys one law in isolation. Pick two, and watch where they actually argue with each other.

Eleven pairs below are argued through directly in the dossier’s own Part 4 and Part 7. Every other combination falls back to the same rule that resolved all of them: grade both, and let the higher-graded law govern structure while the lower-graded one governs only tone — tested, never assumed.

Where two laws meet

Law A

Law B

Hick · SUPPORTEDCalming UI · HEURISTIC

Hick’s Law wants fewer decisions; progressive disclosure wants to defer, not delete. Pushed too far, deferral becomes what Nielsen calls a disclosure cliff — a screen with no first door at all. Rule: hide detail, never hide a decision-critical item (2FA, account deletion, the exit itself).

Challenge · Audit this screen

Open

A settings-and-upsell screen carries six untagged elements. Tap each one and name the law that governs it.

Push notifications

Reminders, mentions, weekly digest

All notification types

Six elements below, each with its own numbered tag. A wrong tag stays wrong until you retap it.

Insight

Intuition is a law you no longer have to remember.

Every screen in the Experience act above got faster to read for the same reason a checkout gets faster to build once you have audited one: the law stopped being a fact you recall and became a shape you just see. That is not a lesser form of knowing the twelve principles — it is what actually applying seventy years of Fitts, or seventy days of your own team’s usability tests, is supposed to feel like from the inside. The grade never goes away. It just stops needing to be looked up.

Mental model

Whenever a design claim in a review arrives wearing the word ‘law,’ ‘effect,’ or ‘principle’,

look for who measured it, on whom, and whether a later, larger look at the same question agreed,

because the citation almost always exists — a real name, a real year — and what gets dropped is the second half: what was actually measured, and what a meta-analysis later found.

Tomorrowgrade one principle from this quarter out loud in your next design review, before you use it to end a disagreement a five-minute test could settle instead.

End of experience

← Back to the constellation

Say “Law”Prove It

Eight Screens, Ten Seconds Each

Design “Laws” Are Not Laws

The Quarter, Week by Week

One Screen, Audited

Law Collisions

Where this idea goes next

Say “Law”Prove It

Eight Screens, Ten Seconds Each

Design “Laws” Are Not Laws

The Quarter, Week by Week

One Screen, Audited

Law Collisions

Say “Law”
Prove It

Say “Law”
Prove It