I’ve read where most of the personality is formed in the first 5 years of life through interactions with adults, usually parents. Since psychosis does involve some kind of external influences being thought about, perhaps it could be the brain still looking for what it needed in those first years but was unable to find. I read they think that infants first feel like they are one with the mother and then later separate to form a separate person. And that a child growing up needs to feel their experience and feelings are known to their parent, who can be trusted and tolerant. There is a lot that can go wrong on the way to maturity. If we really knew what happens to people, maybe we would be a lot more sympathetic.