Forcing Function

Don Norman, a cognitive scientist at the University of California, San Diego, coined the term in his 1988 book The Design of Everyday Things (originally The Psychology of Everyday Things). He defined forcing functions as physical or logical constraints that prevent incorrect actions or require operations in proper sequence, drawing on decades of industrial safety engineering and human-factors research that had applied the concept without naming it. Norman identified three subtypes: interlocks, lock-ins, and lockouts.