I used to believe that writing was the last step. You worked something out, and then you wrote it down so that other people could have it too. Three hundred reflections later, I am fairly sure that has it exactly backwards. Writing is not the record of the thinking. It is the instrument that produces it.
The evidence is available to anyone who tries it. An idea in your head can feel complete and rather good. It has a shape, it seems to connect to other things you believe, and there is a pleasant sense of having understood something. Then you attempt to put it into a sentence, and it falls apart in your hands. The connection you were sure was there turns out to be an association rather than an argument. This collapse is not a failure of writing; it is writing doing its job. The page will not accept a hand-wave, which is precisely why it is useful.
What follows from this is that the discomfort is the point, and that the temptation to write only when you already know what you want to say is a way of avoiding the very thing writing is for. The reflections I have found hardest to write have without exception been the ones where I learned something and the easy ones have mostly been the ones where I already knew. So, as a reflection for today: what do you believe you have a clear view on? And would it still be clear at the end of a page?