What Is Jakob's Law?
Open almost any e-commerce site and the shopping cart icon sits in the top-right corner. Open almost any app and a hamburger icon in the top-left opens the menu. Nobody coordinated this. It happened because Jakob Nielsen's observation is true: "users spend most of their time on other sites." Every visitor arrives at your product carrying a mental model built from thousands of prior interactions elsewhere, and every deviation from that model costs them a small amount of attention to work through.
"Users spend most of their time on other sites. This means that users prefer your site to work the same way as all the other sites they already know." - Jakob Nielsen, Nielsen Norman Group
Mental Models and Convention
A mental model is a user's internal picture of how a system works. They expect the logo to link home, the cart to sit top-right, search to live in the header, and a hamburger icon to hide navigation on mobile. None of these are arbitrary rules handed down by a standards body - they're conventions that won by working, and then kept winning through sheer repetition across millions of products.
When to Follow Convention
- Navigation placement and iconography - back arrow, search magnifier, home icon.
- Form structure and validation patterns.
- Link colour and underlining - blue and underlined is still the most universally recognised link treatment on the web.
- Checkout flow - Amazon and Stripe alone have conditioned hundreds of millions of users on what a checkout should feel like.
- Error and success feedback patterns.
When to Break Convention
Deviation earns its place when an existing convention doesn't fit your specific context, when your product operates in a space with no established pattern yet, or when the usability gain is large enough to justify the relearning cost. The test that actually matters: can a new user figure out the unconventional pattern within seconds, with no instructions?
Key Takeaways
- Users bring pre-built mental models from every other product they've used - work with that, not against it.
- Convention lowers the cost of learning your interface; deviation raises it.
- Innovation earns its place only when it solves a problem convention genuinely can't.
- Test any non-conventional pattern before shipping it - what feels clever in a design review can be a genuine obstacle for a first-time user.
