No one knows what causes dissociative identity disorder. All signs point to extraordinary trauma, particularly during childhood. Some people object to that causation, though, because lots of children who go through traumatic experiences never develop multiple personalities.
On the other hand, not all smokers develop lung cancer.
Childhood trauma, particularly repetitive trauma like physical or sexual abuse, is a notable common thread in a majority of DID cases. According to WebMD, at least 98 percent of people diagnosed with DID experienced extreme, possibly life-threatening ordeals. The hypothesis is that sometimes, these experiences can simply be too much for a child to integrate into conscious experience. The child's brain, as a coping mechanism, essentially "turns off" the conscious identity and creates alternate personalities to experience the pain.
It's possible that some minds are stronger than others, more capable of coping consciously with extreme trauma, so not all children in those situations develop split personalities.
Up next, myth 5: "It's a lost cause."