Users spend most of their time on other websites. They arrive at yours already knowing how the web works — and they expect your site to behave the same way.
Jakob's Law was formulated by usability researcher Jakob Nielsen and states simply: users transfer expectations from one product to another. Every site a person has ever used leaves a trace — a mental model of where things live, what icons mean, how navigation works. When a new site matches those models, it feels instantly familiar. When it doesn't, the user has to stop and think.
This is sometimes framed as a reason to avoid creativity, but that's a misreading. The law doesn't say interfaces should all look identical — it says that convention carries implicit value that needs to be outweighed by a real benefit before you break it. Putting a logo in the top-left corner isn't lazy; it's where every user on earth expects to find it and click it to go home. Replacing the magnifying glass with a custom metaphor for search forces every user to re-learn a gesture they've already memorized on hundreds of other sites.
The leverage point is understanding what users have built their mental models around:
- Position: logo top-left, primary navigation across the top or in a left rail, profile/account top-right.
- Icons: magnifying glass means search, cart means purchase, bell means notifications, hamburger means collapsed menu.
- Behavior: clicking the logo goes home, underlined blue text is a link (or at least clickable), a disabled field is greyed out.
- Vocabulary: "Sign in" vs "Log in" matters less than "Authenticate" which nobody uses.
Conventions are most load-bearing on task-critical flows. A checkout flow that deviates from expected patterns costs real conversion. A marketing page can be more distinctive because the task is exploration, not execution.
The pattern also suggests a useful test: when you're tempted to do something novel, ask whether the novelty serves the user or serves the designer. If the only beneficiary is originality, defer to what users already know.