Design & UX Laws for Product Managers
PMs don't need to be designers. They do need to know why a screen the team loves is going to test badly with users who have never seen it before, and why the beautiful novel gesture someone built in a hackathon is going to tank retention if it ships.
These ten laws explain why. Users spend 95% of their time in other products and arrive at yours with a pre-loaded set of expectations (Jakob's). They can only hold a handful of things in working memory at once (Miller's). They notice the response time before they notice the pixels (Doherty). They remember the peak and the ending of an interaction, not the average (Peak–End). They'll rate a prettier interface as more usable even when it isn't (Aesthetic–Usability).
Use these laws in design review, in the argument about whether to redesign the settings screen, and — most usefully — when someone proposes being novel for the sake of novelty. Save the novelty for the one screen where your product is genuinely different. Use familiar patterns everywhere else.
The 10 laws in this category
- Aesthetic–Usability EffectPretty Feels EasierGood-looking designs feel easier to use than they actually are — which is a real advantage, and a real trap.
- Doherty Threshold400ms or BustWhen the product responds in under ~400ms, users stay engaged. Above that, attention drifts and productivity drops.
- Fitts's LawBig Targets, Close TargetsThe time it takes to tap a target grows with distance and shrinks with size — so the biggest, closest button is the one the product is quietly nudging you to press.
- Hick's LawMore Choices, Slower DecisionsThe more choices you offer, the longer people take to decide — so critical paths should have fewer choices, not more.
- Hyrum's LawThe Law of Implicit InterfacesOnce a product has enough users, someone, somewhere, is depending on every little thing it does — including the things you never documented or intended.
- Jakob's LawUsers Expect What They KnowUsers spend most of their time on other products — so breaking the usual UI patterns costs you more than it earns.
- Miller's LawThe Magical Number SevenWorking memory holds about 4–7 items — so breaking information into groups of 3–5 makes it much easier to read than a long flat list.
- Peak–End RuleMemory Favours the ExtremesPeople remember an experience by its strongest moment and how it ended — which means the last 10 seconds of a flow are worth more than the first 90.
- Principle of Least AstonishmentDon't Surprise the UserThe product should behave the way users expect. A correct spec that surprises people is a support-ticket generator.
- Tesler's LawConservation of ComplexityEvery product has some irreducible complexity. The question isn't whether it exists — it's who absorbs it: the user, an automated system, or your ops team.