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The immediate cause of most memory-lapse failures is interruptions, events that intervene between the time an action is decided upon and the time it is completed. Quite often the interference comes from the machines we are using: the many steps required between the start and finish of the operations can overload the capacity of short-term or working memory.

There are several ways to combat memory-lapse errors. One is to minimize the number of steps; another, to provide vivid reminders of steps that need to be completed. A superior method is to use the forcing function of Chapter 4. For example, automated teller machines often require removal of the bank card before delivering the requested money: this prevents forgetting the bank card, capitalizing on the fact that people seldom forget the goal of the activity, in this case the money. With pens, the solution is simply to prevent their removal, perhaps by chaining public pens to the counter. Not all memory-lapse errors lend themselves to simple solutions. In many cases the interruptions come from outside the system, where the designer has no control.

Excerpted from ‘The Design of Everyday Things’ by Don Norman