Sometimes, I'm curious. I want to know how a mechanism, recipe, or story works. I take a book apart and try to recreate it, all the while figuring out how I might teach it. But then there's the car. I don't want to think about learning how to fix it myself. I just want to get somewhere. And I'm never going to teach auto shop. So, the goals are different. In the first case I am curious about the process. In the second case, I don't care. Interest matters. I have to want to know.
Making books and art is a quest, an expedition, an exploration of new territory. Curiosity can drive the project. In the essay "The Stalin in the Soul" from her excellent book The Language of the Night Ursula LeGuin wrote, "When you start screaming you have stopped asking questions." This sentence has caught me many times in the middle of frustrating projects. I've had to back up and figure out what was propelling me forward before and what needs to happen now to get me going again.
When you get stuck making a book, try to figure out the questions. They might be structural, such as do you make one page fold-out or do you make all the pages wider? If you are just beginning to work on a new book and don't know what it's about yet, pay attention to your day. In an overheard conversation you might wonder why that clerk is so angry, or you might see a box of dolls on a curb, and imagine why the owner is letting them go. Questions beginning with "why" can change your direction, encourage you to go deeper, and to think beyond the obvious.
Asking questions can restart your process. Try making a list at the end of every day of the things you were curious about. Then see if one would make a good book.
And why not?