I'm not sure how others write, but I can't do anything without an outline.
It's a great way to combat "white page syndrome" which is that overwhelming feeling you get at the start of a book where you have nothing, know you need 50+ pages and just go "oh shit... I can't do this".
I run into that even on books I have planned out well in advance, talked to the boss about and have a full-fledged plan for. It's a matter of having a place to start.
So I do an outline, and then slowly fill it in.
Now if I could find a way to combat the utter feeling of disgust I get at the end of a project, where there's just a little left to do and you're absolutely sick of a book and sure it's the worst thing you've ever written, then I could give up beer and coffee entirely.