While schizophrenia might not be " multiple personalities, " you can learn what that actually is by watching our episode on Dissociative Identity Disorder.
In the case of dissociative identity disorder, the goal of therapy is to facilitate fusion of identities, where a person's personality states are integrated and the person feels more whole.
And one idea is that it's abuse plus some sort of genetic or biological predisposition to dissociate and in fact, people with dissociative identity disorder seem to be very susceptible.
Dissociative amnesia is when a person blocks out or forgets important personal information that most people would remember for a lifetime, like where they lived as a child, or what their mother looked like.