To create worry humans elongate fear with anticipation and memory, expand it in imagination and fuel it with emotion. The uniquely human mental process called worrying depends upon having a brain that can reason, remember, reflect, feel, and imagine. Only humans have a brain big enough to do this simultaneously and do it well.

Worry: Controlling it and Using it Wisely (ed. Pantheon, 1997) - ISBN: 9780679442370