Shirley Mason aka Sybil LIED! The entire book/movie was based on lies. 
"Shirley Mason was the psychiatric patient whose life was portrayed in the 1973 book Sybil. The book and subsequent film caused an enormous spike in reported cases of multiple personality disorder.
Mason later admitted she had faked her multiple personalities."⬅️⬅️⬅️⬅️⬅️