From Raising Cain
[Dr. Waldheim tells the detectives about multiple personalities
All multiple personality patients, regardless of the differences in their background, seem to share certain childhood traumas. When these occur, the original personality splinters into others. For instance, if a boy is molested by his mother or abused by his father, the original...
[the detectives grab Waldheim from going the wrong way
] Ah. The original personality forgets it ever happens. How could his loving parent do such a terrible thing? And he creates an alternate personality. This becomes the person it happened to. He is the one who suffers the pain for all the rest.