Writing is an evolving process, even as you do it. It evolves beneath your fingers as you type. A writer should not resist this. Allow your writing to change and contradict itself temporarily so you can learn from the contradictions.
Even messy things like contradicting yourself can help you understand your thought processes more thoroughly. The value in this kind of failure lies in the potential of learning WHY you write what you do. Why do you make the mistakes you make? This is the same thing a basketball player is doing when he/she watches and re-watches footage from the last game — mistakes and all. So, for instance, if you look back over your writing “footage” and find that your thesis and the body of your draft are not matching up, you can find out which one needs to bend, and bend it.
Be bold enough to deliberately and resolutely reject the limited, pragmatic, “X marks the spot” notion of writing that we educators have helped create, in which being perfect and complete is the only and tyrannical goal of composition.
Arriving at a “correct” Final Draft is only ONE of the purposes of writing. Like dancing or performing music, the getting-there is just as important as the arrival.