Users spend most of their time on other sites.
People spend most of their time on other sites, so they expect yours to work the same way. Follow convention — and watch closely, because AI is rewriting what convention means.
Jakob Nielsen — the same Danish usability engineer behind the ten heuristics — stated his law of the internet user experience in 2000, at the height of every site inventing its own navigation.
The law is an argument from arithmetic: users spend nearly all their time on sites other than yours, so your site is the exception to their habits, not the rule. Familiarity is a feature you get for free by following convention.
Users spend most of their time on other sites, so they expect yours to work the same way. Break convention only where the payoff clearly outweighs the relearning cost.
Users form their mental model of how an interface should work from every other interface they’ve used. The closer yours matches that accumulated expectation, the less they have to learn — and the more usable it feels.
Every product a user has touched leaves a deposit of expectation. They arrive at yours already “knowing” where the cart, the search, and the menu should be — because a hundred other sites put them there.
Logo top-left links home. Cart top-right. Primary nav across the top. Underlined blue text is a link. These aren’t laws of nature — they’re conventions so widely shared they may as well be.
A “creative” date picker, a novel scrollbar, a bespoke dropdown — these almost always cost more than they’re worth. Familiar controls work because users have thousands of reps with them already.
Users don’t read your UI fresh — they match it against an internal model built from experience. When your interface matches the model, it feels intuitive. When it conflicts, it feels broken.
Convention isn’t a cage. Break it only when the gain clearly outweighs the cost of re-learning — and when your new pattern is so much better that it could become the next convention.
AI is rewriting the conventions users carry with them. The reference point is shifting from “every website” to “every AI tool.”
ChatGPT trained hundreds of millions of people on a single pattern: a message box at the bottom, streaming responses above, a thumbs up/down. That’s now an expectation users bring to every AI feature.
Users increasingly expect to type what they want instead of hunting through menus. The command palette and the AI prompt are converging — “tell me what you need” is becoming the new front door.
AI can generate a different interface for every user — the opposite of Jakob’s Law’s call for sameness. The tension is real: personalization boosts relevance but erodes the shared conventions users rely on.
Jakob’s Law still holds — but the body of “other sites” it points to is changing fast. The safe baseline now includes AI affordances: a prompt box, streaming output, “regenerate,” cited sources, and an undo for anything the model touched.