Laws & Effects
Descriptive principles: they explain why users behave as they do. Use them to predict the consequence of a design choice before you commit to it. Each entry gives the idea in original wording, the design consequence, and the trade-off to watch.
Contents
- Fitts's Law
- Hick's Law
- Miller's Law
- Jakob's Law
- Tesler's Law (Conservation of Complexity)
- Aesthetic-Usability Effect
- Doherty Threshold
- Goal-Gradient Effect
- Peak-End Rule
- Serial Position Effect
- Von Restorff Effect (Isolation Effect)
- Zeigarnik Effect
Fitts's Law
The time to move to and acquire a target grows with distance and shrinks with target size. Big, close targets are fast; small, far ones are slow.
Consequence: Make frequent or important targets larger and place them near where the pointer or finger already is. Primary actions deserve size and proximity; destructive actions can be deliberately smaller and farther to slow people down.
Trade-off: Enlarging everything destroys hierarchy. Size is a finite signal — spend it on what matters most. Note that the practical minimum size depends entirely on the input device; see the medium skills for the actual numbers (a cursor is effectively one pixel; a fingertip is not).
Hick's Law
The time to make a decision grows with the number and complexity of the choices.
Consequence: Reduce the number of options presented at one moment. Break long lists into categories, hide advanced options behind disclosure, and lead users down a guided path rather than presenting everything at once.
Trade-off: Hiding options reduces immediate cognitive load but can cost discoverability and power-user speed. The right cut depends on how often each option is actually used.
Miller's Law
People can hold only a handful of items in working memory at once (the popular "7±2" is better treated as roughly four chunks for reliable design).
Consequence: Chunk information. Group related fields, segment phone numbers and IDs, and don't ask users to remember something from a previous screen to use on this one. Carry context forward instead of taxing memory.
Trade-off: Over-chunking can fragment a task into too many small steps. Group by meaning, not just to hit a number.
Jakob's Law
Users spend most of their time in other products, so they expect yours to work like the ones they already know.
Consequence: Honor established conventions for common patterns (where the nav lives, what a trash icon does, how search behaves). Familiarity is free usability. Innovate where it adds real value, not on the plumbing.
Trade-off: Convention can entrench mediocre patterns. Deviate only when the gain clearly outweighs the relearning cost — and note that "convention" here means broad cross-product familiarity, not slavish per-OS idiom-matching.
Tesler's Law (Conservation of Complexity)
Every system has an irreducible amount of complexity. The only question is who absorbs it — the user or the design.
Consequence: Move complexity into the system wherever possible: sensible defaults, inference, automation. Don't push work onto the user that the application could do itself.
Trade-off: Absorbing complexity can remove control or transparency. Some complexity belongs with the user because they need to own the decision; hide the rest.
Aesthetic-Usability Effect
People perceive attractive interfaces as easier to use, and are more tolerant of minor problems in them.
Consequence: Visual polish is not decoration; it buys goodwill and forgiveness. But it can also mask real usability problems in testing.
Trade-off: Don't let attractiveness substitute for actual usability. Pretty can hide broken — test for real task success, not just impressions.
Doherty Threshold
Productivity and engagement stay high when system response to user action is faster than roughly 400ms; beyond that, attention and flow degrade.
Consequence: Keep interactions feeling instant. When real work takes longer, show immediate feedback (optimistic UI, skeletons, progress) so the perceived response stays under the threshold.
Trade-off: Faking speed with animation can backfire if the underlying delay is large and the user is left waiting after the animation ends. Match the feedback to the real duration.
Goal-Gradient Effect
Motivation increases as people get closer to a goal; visible progress accelerates completion.
Consequence: Show progress (steps completed, "2 of 3"), and consider giving a head start (a partially complete progress bar). People finish what looks nearly finished.
Trade-off: Fake or padded progress erodes trust once noticed. Keep the gradient honest.
Peak-End Rule
People judge an experience largely by its most intense moment and its ending, not the average.
Consequence: Invest in the emotional peaks (the moment of success, the "it worked") and the endings (confirmation, completion, sign-off). A graceful finish outweighs a dozen forgettable middle steps.
Trade-off: Don't neglect the middle to the point of frustration — a bad enough trough becomes the peak that's remembered.
Serial Position Effect
People remember the first and last items in a series best; the middle blurs.
Consequence: Put the most important navigation items and actions at the start or end of a list or bar, not buried in the middle.
Trade-off: Only a few positions are privileged; don't try to make everything "first or last."
Von Restorff Effect (Isolation Effect)
The item that differs from its neighbors is the one that gets noticed and remembered.
Consequence: Make the single most important action visually distinct (one primary button, not five). Distinctiveness is how you direct attention.
Trade-off: If everything is emphasized, nothing is. Each added highlight dilutes the others — emphasis is zero-sum.
Zeigarnik Effect
People remember incomplete tasks better than completed ones, and feel tension to finish them.
Consequence: Use visible "unfinished" cues (checklists, incomplete profiles, "1 step left") to draw users back to completion.
Trade-off: Manufactured incompleteness feels manipulative. Use it for genuinely valuable tasks the user wants to finish, not to trap attention.
Further reading (do not copy verbatim)
Jon Yablonski's Laws of UX (lawsofux.com, and the O'Reilly book) is the best-known collection of these and is licensed CC BY-NC-ND — cite it, link it, but write your own descriptions as above rather than reproducing its text.