Paraphilias (e.g., pedophilia, fetishism) are said to be virtually ineradicable once established. The authors propose that the motivational state known as the Zeigarnik effect, according to which interrupted tasks are better recalled than completed tasks, may provide understanding of this process, especially its later addictive-compulsive quality. Reasoning from Zeigarnik-type research, the authors predict a relation between early sexual arousal, its frustration, and subsequent events associated with such arousal. The paraphilias are thus seen as an unusual by-product of a normal adaptive process, that is, a tendency to privilege the recollection of unfinished over finished activities. The authors discuss why paraphilias are associated nearly exclusively with males, and why paraphilic tendencies are apparently quite rare in traditional societies. They also propose new research on the processes and outcomes entailed by the Zeigarnik effect, such research including, but not being limited to, sexuality.