Truddi's therapist, Dr. Robert Phillips, says what causes a personality split like Truddi's is unclear. "It seems to be something about the brain, about the mind, which allows this very creative process to come in and to help defend a person. It usually is a person who is abused very, very young—before personality is formed," he says. "When you're so young everything is overwhelming; the whole world is overwhelming. Something like this just overloads, so the person cannot stay there and take it."