I don't think it's a mystery. You get told enough times that you're a piece of ****, you start to believe it. You get abused by authority enough, you get hyper-vigilant to further abuse. You learn that abuse can be prevented by deferring, you start to preemptively defer.

In short, it comes down to a learned pattern of thinking and behavior where you assume that others have authority, expect them to abuse it, and try to protect yourself by knowing your place.

When this pattern no longer becomes adaptive because your circumstances change, you get lots and lots of therapy.

For me, personally, the most healing (non-skills based) aspect of therapy has been the novel experience of not having someone in a position of authority (authority assumed and conferred based on status as middle-class, educated, white, male) **** with me.