Like the fire protection and emergency exit systems of a building, digital products must also be built so that when something does go wrong, harmful effects are minimized or prevented through error response and recovery.

Errors can occur on many levels. Some, like broken links or programming glitches, are a matter of writing valid code. Others occur because of confusion about how things work, or through simple mistakes, like clicking on the wrong menu item when your elbow is jostled, or poking a small screen. There is no such thing as a fail-safe system. No interface is intuitive to every user, and no user is on target every time.

Designing for contingencies is about using design to minimize the impact of errors and system failures when they can’t be avoided.

Sarah Horton and Whitney Quesenbery.