You can trust logic;

Not from flawed premises, you can't. And most of the premises people typically assume about their own motivations are seriously flawed. Thus, people can use perfectly valid logic to construct reasonable, elegant theories about their behavior that are nonetheless 100% irrelevant to how they're actually generating those behaviors.

you can't trust that your brain is logical.

Actually, your brain is logical, in the sense that a computer is - it does what it's programmed to do, even if what it's programmed to do is stupid. ;-)

I did the former.

I should probably clarify what I mean by "distrust logical answers". I should've said, "distrust logical answers to emotional or experiential questions", or "distrust 'far' answers to 'near' questions". The question of one's motivation for doing a thing is "near", so generating an answer from the "far" side of the brain is pure confabulation. Thus, a logical, abstract, sophisticated answer to that question is not actually an answer to that question.