Memory filters in the mind are designed to help individuals access their past life skills and talents without connecting with the "past life personalities" who earned them. What normally happens is, when an individual is in crisis, they access the "unused" part of their brain (where all their past life data is stored) to help them overcome it. Often the past life personality was an integral part of exercise of the talent or skill, which is why the mind needs to filter out the "personality" from the "learned skill or talent". When the crisis is averted, the pathway to that part of their brain is automatically shut off by the mind's past life filters.

In Multiple Personality Disorders (MPD), the crises are either so severe or so chronic and long lasting that brain filters of old personality will no longer function properly. The mind then has difficulty distinguishing between the current and all prior personalities. In a sense, the prior personalities come back to life and fight for the attention of the current body-mind. In MPD, a host of prior personalities jockey for position at the forefront of the person's awareness and end up "taking turns".

Some cases of MPD is said to have resulted from severe, ongoing emotional, sexual, or physical abuse.  Although, it hasn't been proven, it is simply a guess. The process seems to begin during childhood when it is during this time that personality develops and these could cause alternate, distinct personalities to form.