I think the simplest way to explain it to people is simply to say little blips of amnesia or memory loss.

A toddler gets traumatized severely and goes into a "shock" type state. Now you have to understand that it does not take much to traumatize a newborn to four year old toddler. Anything that scares the toddler enough can put the child into shock. Anything that causes severe enough emotional pain can put the child into shock. And, of course, anything that causes severe physical pain can cause the toddler to go into shock. But it is how the toddler perceives the issue! What I am saying that many adults have no empathy about a toddlers emotional and psychological issues. My parents didn't and that is why I have a dissociative disorder.

The dysfunctional family totally ignores the toddler's feelings and continues to traumatize or abuse the child during the toddler years. So the toddler is triggered into that state of shock regularly during the toddler years. That state of shock is exactly like a state of hypnosis. Depending on many factors different personalities can develop in that state of shock/hypnotic state.

In my case where the physical abuse was not too extreme but continual, the alters are not extremely different. My parents were dysfunctional but not total psychopaths. So far me it is more like memory problems than different personalities. A layman would not be able to recognize the differences in my personalities.

But there is an automatic amnesia effect that occurs when a person switches into and out of that state of shock/hypnotic state. The memories are lost or not processed correctly.