I'd Forgotten What this Was Like
It's also a sense that you are not just working with a mass of unformed clay, you're pretty much producing that clay, in that unformed state. It's knowing that you've just written a bland scene and fighting off the temptation, pull, need to go back and "fix" it, because you haven't written enough to know yet what that fix would be. It's leaving bracketed placeholders for info you don't have yet--descriptions, settings, historical details. Lots of bracketed placeholders.
And it's a piling up of pages in the binder, pages that give you at once an incredible sense of accomplishment and, at the same time, shout at you that you'll be doing them all over again, so, please, don't get too excited here.