I know where this feeling started. Why won't it leave?

You did the work. You found the root — some early proof, some voice, some room where you learned to doubt yourself. This is more than most people manage. But notice what you have now: a clear diagnosis, and the same old flinch, still firing. This is where people stall. They mistake insight for cure. They keep excavating, hoping one more layer of understanding will finally silence the feeling. It will not. The feeling runs on habit, not on evidence. You cannot think your way out of a habit. You act your way out. So the question changes. Not "why do I feel this way" — you already answered that. The question is: what will you do in the next hour, at your desk, in that meeting, regardless of what the old voice says? That is the only place this gets settled.