i think in relation to "parts" it's not really this "multiple personality" thing, like sybil or f*ckin' eve. it's just. different things are fronting, we section our awareness of ourselves into tangible elements. fractured, y'know, faceted.
i've met people w/o dev. trauma who have this, too. when i was right in it. they were older, fell into it. you can tell, you can see. they're unpredictable, they're contradictory. bad tempers. where's the explanation? same, same, same. punched a garbage can once at work. guy was walking by, me, just slow-motion punching a garbage can. still got the mark on my knuckles. why? mad. the rage flows through me, becomes me, turns me.
i think it's just a certain type of trauma. executive functioning, mind-casting over, living, breathing shit. secondary trauma, y'know. take-good-care. there's a certain formation aspect, maybe like because you're needing to form something new, something purely for it, when you're in that kind of trauma space. because it's so outside of your experience, there's no native function.