I was listening to an interview with the author of a new book about how successful sports figures pull out of a slump, and he made the most interesting (and true, I thought) point. He said they all believed in their abilities and committed to success, even if it wasn't looking good for either. When they didn't have that confidence level, they lied to themselves. Yep, despite their failures, they told themselves they could do it and they focused, sustaining their commitment with whatever it took. I like that idea.
Writers can generally find an excuse, any excuse, to escape writing. It's not good enough, I can't get it right, the characters are flat, the plot stupid, the market won't be ready for it. . . I can probably come up with a list of a hundred off the top of my head, but that'll just delay getting today's writing done, and heaven knows, I can invent easier ways to do that, LOL. The point is, a writer has to believe, and believe strongly, in the book and in her ability to get it done. Rewrites are the ultimate horror for me - I find I lose the vision of the book too easily when I become ensnared by the minutiae of phrasing, verbs, cutting adverbs, etc. During that process, especially, I need to keep my belief in the book bolstered. (And my alliteration to a minimum!)
Being committed to making a book the best it can be involves the boring and painful parts as well as the fun of its creation.
And as Winston Churchill said, never, never, never, never give up. Never.