On rare occasions, people actually develop a true Multiple Personality Disorder, which is a complex, chronic form of post-traumatic dissociate psychopathology. However, anyone who has experienced abuse may selectively create personalities in [his] mind as a means of escape.
Children who use this coping device have extraordinary imaginations. When a child who has been abused encounters overpowering emotions, he may choose to escape into a safe personality, one who hasn't been abused. . . to detach himself from the memories and pain.
Many normal children play with imaginary companions; abused children can use such creative resources to a pathological extent, in extreme cases falling prey to MPD.
(Nobody Understands My Pain: Dealing with the Effects of Physical, Emotional, and Sexual Abuse by Linda Harriss, Friendswood, TX: Baxter Pres, 2004, page 121. Used by permission.)