I always have a goal when I write a book, to finish ;) Cheeky, huh?! Seriously, I find it helpful to have some sort of goal and I develop a loose plan accordingly. With my WIP R, I had a goal of 20 chapters and 50,000 words. Now this is just something to reach for, particularly the word count. If I go over the word count I don't mind a bit. If I come under, I'm disappointed. As for chapters, I follow a standard format for a 20 chapter book, but consider it a loose guideline and not set in stone. And while I have a general idea of what I want to happen each chapter and generically what should happen, I am certainly not bound by it. Particularly in the second draft I allow myself to see structurally what is better for the story.
All this is helpful to keep me on track. I need that because the meat of the story is something I think out more in detail as I write the story. And so, as I go, I often feel so close and yet so far from THE END.
Anyway, here's an update: 41,083 word count and I'm in the middle of chapter 16 struggling to "make it, as in the story, BIGGER."
Fight your fight. Keep on!