While DID is a rare reaction to brain trauma, most people are familiar with the concept of repressing negative memories. "Some aspects of experience are too unbearable for a person to survive," she says. "When that happens, a part of the person can capture those memories and keep the rest of the person safe by holding onto those and isolating them. ... The body remembers it, but it's not pushed away—it simply holds onto it and doesn't share it."