UX Laws & Cognitive Principles

The mental models and behaviors from the previous pages have been distilled into a set of named laws — rules of thumb, drawn from psychology, that predict how people perceive and use interfaces. None is absolute, but together they’re the closest thing UX has to physics. Here are the ones worth knowing cold, each with the one move it implies.

The quick reference

Law	In one line	Apply it by
Hick’s Law	More choices → longer decisions	Reduce or group options
Fitts’s Law	Bigger + closer targets are faster to hit	Make key buttons large and near
Miller’s Law	Working memory holds ~7±2 chunks	Chunk content into groups
Jakob’s Law	Users expect you to work like other sites	Use familiar patterns
Law of Proximity	Close things are seen as related	Group with spacing, not just lines
Zeigarnik Effect	Unfinished tasks nag at us	Progress bars, checklists
Peak–End Rule	We judge experiences by the peak and the end	Nail the highlight and the finish
Aesthetic–Usability	Pretty things are perceived as more usable	Visual polish builds trust
Doherty Threshold	Keep responses under ~400ms	Fast feedback, optimistic UI
Serial Position	First and last items are remembered best	Put key items at the ends
Von Restorff Effect	The different one is remembered	Make the primary action stand out

The rest of the page unpacks the highest-leverage ones.

Hick’s Law — fewer choices, faster decisions

The time to make a decision grows with the number and complexity of options. A menu of 30 flat items paralyzes; the same items in 5 groups of 6 are easy.

Apply it: cut options, or chunk them into categories. Reveal advanced choices progressively. A single, obvious primary action beats a row of five equal buttons.

Fitts’s Law — big and close beats small and far

The time to hit a target depends on its size and distance: bigger, nearer targets are faster and more reliable to click or tap. A corollary loved by designers: screen edges and corners are effectively infinite in size (your cursor stops there), which is why menu bars live at the top edge.

Apply it: size buttons by importance; keep primary actions large and within easy reach (the thumb zone on mobile); park global controls at edges/corners.

Miller’s Law — chunk it

Working memory holds only about 7±2 items at once (and honestly, plan for fewer). This is why phone numbers are grouped and why a 20-field form feels crushing.

Apply it: break long content, forms, and menus into small labeled groups. Chunking is why “0821 · 4455 · 9910” is readable and “082144559910” isn’t.

Law of Proximity — space groups things

A Gestalt principle: elements placed close together are perceived as belonging together — more powerfully than boxes or lines. Whitespace is your grouping tool.

Apply it: group related fields, actions, and content with spacing before you reach for dividers or boxes. Related things near; unrelated things apart.

Zeigarnik Effect — unfinished business sticks

People remember incomplete tasks better than finished ones — an open loop creates a small tension that pulls them to close it. Progress bars, checklists, and “profile 60% complete” nudges all exploit this.

Apply it: show progress through multi-step flows; a visible “3 of 5” or a checklist makes people want to finish. (Use it to help users complete their goals — not to trap them.)

Peak–End Rule — the highlight and the finish

People judge an experience not by its average but by its most intense moment (the peak) and its end. A signup that’s tedious throughout but ends with a delightful “you’re all set!” is remembered fondly; a great flow with a broken last step is remembered as broken.

Apply it: invest in the emotional peak (a moment of delight or accomplishment) and especially the ending — success screens, confirmations, the last thing they see. Don’t let the finish be an afterthought.

Aesthetic–Usability Effect — polish reads as quality

Users perceive attractive interfaces as easier to use — and are more forgiving of minor problems in them. Visual craft isn’t decoration; it directly shifts how usable and trustworthy the product feels.

Apply it: spend real effort on visual polish. It buys goodwill and trust — but it’s not a substitute for actually working, just a multiplier on it.

Von Restorff Effect — make the one thing pop

The item that stands out from its peers is the one remembered and acted on. If every button looks equally important, none is.

Apply it: give a screen one clear primary action, styled distinctly; demote everything else. This pairs with the dashboard hierarchy principle — one thing should win the eye.

Doherty Threshold — stay under 400ms

When the system responds in under ~400ms, people stay in flow and actually work faster and more happily; past that, attention drifts. Speed isn’t just nice — it changes behavior.

Apply it: keep interactions snappy. Where you can’t, fake it with perceived-performance tricks — optimistic updates, skeletons, instant feedback — so it feels under the threshold.

Serial Position Effect — the ends are remembered

In a list, people best remember the first and last items (primacy and recency). The middle blurs.

Apply it: place the most important navigation items and actions at the start and end of menus and lists, not buried in the middle.

Using the laws well

These are lenses, not laws of nature. They point you at likely improvements, but they can conflict (Hick’s says fewer options; a power user wants more), and the only real arbiter is testing with actual users (who won’t behave as you expect). Use the laws to form good hypotheses — then watch real people and let reality win.

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A great, well-cited catalog of these is Jon Yablonski’s Laws of UX, and the research-backed source for most of them is the Nielsen Norman Group.