Write to think, not to record. Most good ideas don't exist until you write them.
I used to think writing was something you did after you had the thought — a way to capture something that was already formed. It's almost the opposite. Writing is where the thought gets formed. The blank page is where you find out what you actually think, as opposed to what you vaguely feel.
There's a specific kind of idea that only shows up under the pressure of putting words together. It resists being summarized in advance. You have to work toward it through sentences, follow the thread, and sometimes end up somewhere completely different from where you started. That's not a failure of planning — that's the work.
This is also why I don't write to perform. The posts that feel most alive to me are the ones where I figured something out in the writing itself. The ones where I knew the conclusion before I started tend to be the flattest.