Design pattern

A design pattern is a reusable solution to an interface problem that comes up often. It is a convention, a way of solving a problem that enough products have adopted for users to recognise it and know how to use it without having to learn it. Tab navigation, the multi-step form with a progress indicator and the confirmation dialog before a deletion are common design patterns.

Because users do not have to relearn an interaction for every product. A recognised pattern draws on what they already know how to do. That is the point of Jakob's law, formulated by Jakob Nielsen: users spend most of their time on other services and expect yours to work the same way. Inventing an interaction only makes sense if the existing patterns answer the need poorly.

The platforms' official guides are the most stable source: Apple's Human Interface Guidelines for iOS and Google's Material Design for Android document the patterns recommended on each mobile system. Public design systems are another, with components that embody these patterns and their usage rules. There are also online libraries that gather screenshots of real products, useful for observing how the same problem is handled from one interface to the next.

The design pattern is the principle, the way of solving an interaction problem, independent of any technology. The design system is its concrete implementation in a given product, in the form of documented components paired with usage rules. So a design system contains components that embody patterns, specifying in which contexts to use them.

It is a design pattern that uses the user's familiarity against their own interest. Unsubscribing made deliberately difficult, a pre-ticked box that commits them without their knowledge, an accept button given prominence while the refusal is hidden. They work precisely because they use familiar conventions. So recognising a pattern never removes the need to judge what it does to the user.