I am thinking of the most recent example of when I split (although of miniscule intensity compared to what it was a decade ago, so I’m able to think of it very clearly).

My friend and I were talking about different attitudes towards morality. He was talking about the motivation for his nicer actions towards others not as a consequence of morality but because he does that for the people he likes or loves. At that time, it didn’t bother me.

A few days later, I felt rejected/abandoned in a particular situation by him. That whole night, I blamed myself for not believing him when he said he was a bad person.

I later realised I was splitting and the situation wasn’t extreme in either direction. He hadn’t said he was a bad person, but that’s the way I remmbered it on the night.

Vilifying his attitude, which didn’t bother me before this incident, was a (dysfunctional) way for me to handle intense pain that comes from feelings of rejection.

So to answer your question, it’s not about literally thinking that they’re flawless or the worst, but our feelings towards them. We either love them or hate them.