Laws of UX & Cognitive Principles

Laws of UX & Cognitive Principles

These are not style opinions. Each "law" is a named finding from perceptual psychology, cognitive science, or behavioral economics that constrains how every human uses every screen — desktop, mobile, watch, voice, kiosk. Jon Yablonski's Laws of UX (lawsofux.com, 2020) collected the design-facing subset; the originals trace to the researchers credited below. Cite the source when you invoke a law in a design review — "this fails Fitts" lands harder than "the button feels small."

Read each law as a fixed five-part block: Origin (who/when), Principle (the mechanism, with the math where it exists), In the UI (one concrete control or screen), Implication (the general rule you derive), Pitfall (the failure mode). Keep "In the UI" and "Implication" distinct: the first is an example, the second is the rule.

The laws also combine — most good interactions satisfy several at once and most bad ones violate a cluster. A fast, optimistic submit serves Doherty and Flow; a forgiving, system-parsed input field serves Postel and Tesler and Recognition-over-recall. When two laws appear to conflict (Hick says fewer choices, but Jakob says match the conventional five-tab bar users expect), Jakob usually wins for plumbing and Hick for content — convention is a learned default that costs nothing, novelty is the expensive part.

1. Targeting & decision laws (the geometric ones)

Fitts's Law

• Origin: Paul Fitts, 1954. Formalized in The information capacity of the human motor system.
• Principle: Time to acquire a target = T ≈ a + b·log₂(2D/W), where D = distance to target, W = target width along the motion axis. Acquisition time grows logarithmically with distance and shrinks as the target gets bigger. Doubling size helps far more than the formula's modest log on distance suggests in dense UIs.
• In the UI: A primary CTA rendered 48px tall and placed near the user's current focus is hit fast; the same action as a 16px text link in a far corner is slow and error-prone. Screen edges and corners have effectively infinite width (the pointer stops dead) — macOS menu bar, Windows Start corner, the right-click context menu spawned at the cursor (D≈0).
• Implication: Make important, frequent targets big and near. Anchor destructive or rare targets far and small. Exploit edges, corners, and the pointer's own position for the loudest actions.
• Pitfall: Tiny icon-only buttons crammed together (toolbar of 24px glyphs at 4px gaps) — every click is a coin-flip. Also: a big visual button with a small hit area (padding outside the clickable region) silently breaks the law.

Hick's Law (Hick-Hyman Law)

• Origin: William Edmund Hick and Ray Hyman, 1952 — independent papers, jointly named. Don't drop Hyman.
• Principle: Decision time rises logarithmically with the number of equally-probable choices: RT = b·log₂(n + 1). Each doubling of options adds a roughly constant slice of deliberation, not a linear pile.
• In the UI: A checkout with one obvious "Pay" button decides instantly; a settings page dumping 40 toggles at once stalls the user. Chunking the 40 into 6 labeled groups, or revealing advanced options behind a disclosure, restores speed.
• Implication: Reduce or categorize choices. Use progressive disclosure, smart defaults (a pre-selected sensible option removes the decision entirely), and grouping. Highlight a recommended path so the user can skip the comparison.
• Pitfall: Over-applying it into death-by-wizard — splitting one coherent choice across ten one-question screens adds navigation cost and hides context. Hick's targets count and grouping, not "fewer screens always."

2. Memory & cognition laws

Miller's Law

• Origin: George A. Miller, 1956, The Magical Number Seven, Plus or Minus Two.
• Principle: Working memory holds ~7±2 chunks, not items. The number is about units of meaning, and a chunk can be large (a familiar acronym, a grouped phone segment). Nuance/myth: "7" is widely misquoted as a hard cap on menu items or nav links — it is not. Cowan's later work (2001) refines the real span to ~4 chunks. The usable lesson is chunk and group, not "never exceed seven."
• In the UI: A phone number shown as +1 (415) 555-0132 is four chunks and trivially held; +14155550132 is twelve digits and slips. Card numbers grouped in 4s, OTP fields in segments, nav grouped into labeled sections.
• Implication: Format and group information into meaningful chunks so the user holds a structure, not a stream. Don't make the user keep facts in their head across steps — show them on screen (recognition over recall, §5).
• Pitfall: Citing "7±2" to justify capping a menu at seven links, or worse, padding to seven. Navigation breadth is governed by scanability and labeling, not this number.

Jakob's Law

• Origin: Jakob Nielsen, 2000.
• Principle: Users spend most of their time on other sites and apps. They form mental models from the aggregate, and they expect yours to work the same way. Familiarity is transferred expectation.