When writing, or researching (or indeed writing up research), one of the biggest challenges is getting the mix right between the big picture and the fine detail. On the one hand, it's easy to get so caught up in creating wonderful individual scenes, or in picking apart individual points of argument, that the overall story is lost. At the other extreme, it's easy to get so caught up in the big idea that you lose track of the little details that make it work perfectly.
Currently, I tend more towards the latter, trying to focus on a core idea and sometimes pushing it too hard. It wasn't always the case, and I have phases when I get caught up in the details, too. My strategy for dealing with it seems to be a combination of trying to write in the right sort of mood, and making use of focussed re-drafts to fix mistakes.
Sometimes though I wonder if the emphasis on re-drafting is the right one. Re-working is a wonderful thing, and absolutely necessary in almost every case. Even so, I suspect that a basic core of things needs to be right from the start. That's partly why I'm so focussed on the big stuff; structural elements are much harder to change than elements of detail. If you're saying 'I'll sort the plot/thesis out in the next draft' that's a lot harder than if you're trying to get some more detailed descriptions in.
That said, I suspect that in one way whatever bit we leave out turns out to be the difficult bit. It will be, almost without exception, the bit of writing we don't like, and so gloss over. So we're left with hours of doing precisely the bit we like least, and that's never easy. Hmm... maybe we should get some interesting bits wrong deliberately, to give ourselves something fun to fix?