I've thought about these things a lot also. Doubt is the solvent of the psyche. Question anything and you dissolve your faith in it. My default position is to question, and so anywhere I point my consciousness I dissolve all faith in what I behold.

For me I don't know why that is exactly - I have hypotheses,bit nothing concrete - but for a person who knows they have a complex traumatic past it comes from a constant need to interrupt expression with self-reflection. You have to question your impulses before they flow out of you because allowing them to flow outward meant facing recrimination. So in order to avoid external recrimination you become your own surveillance police:

You have an impulse, stop the impulse, look at the impulse questioning whether its expression would lead to recrimination... By that point it doesn't matter whether letting the impulse go would have met with recrimination or not, because the impulse is already lost and you've already given up your chance to express and enjoy that moment.

By questioning yourself in this way you gradually dissolve the natural progress of desire to impulse to expression, and nothing you do is fulfilling, and nothing has meaning, and you've dissolved all the threads of meaning that would have woven you into a real person. What you're left with is a vast mess of patchwork pieces of self, broken apart and strewn about in chaos where there aught to be a cohesive quilt.