Questions, questions, questions. No matter the stage of the writing process, questions attend you like handmaidens.
In the conception stage, you may wonder: Is this idea worthy of a book? Do I have what it takes to write it? Do I have the right to tell this story?
In the writing stage, you might ask: Is this any good? What is this character's motivation? How do I get the story to move from here to there? Will anyone want to read this? How much further do I have to go?
In the editing stages, you and your editor might ask: What other stories belong here? What's missing? What if we moved this part over there? Is this the right voice for the book? What are the stakes? Is this what you mean? Can we simplify this?
The questions continue. Sometimes it helps to name them out loud. Naming them clarifies the current problems to (eventually) be solved, and it also relieves their psychic weight.
So, I'll ask you: What are your questions about your book right now?