] What is undoubtedly true is that memory, like everything
] else in biology, is an evolved, functional response. If
] individuals tend to be better off by not remembering
] certain things, natural selection will tend to construct
] their brains that way. Indeed, the existence of
] post-traumatic stress disorder suggests that individuals
] are better off without those memories. And in fact, most
] people do come out of trauma with their psyches intact,
] so it is possible that what has happened to PTSD
] sufferers is that the memory-prevention mechanism has
] gone wrong.

Memory and emotion