Sometimes I get 'writer's block'. I'll be working through the book, making small edits, then I just can't think anymore. It does happen :). I tend to mostly work on the book when I have lots of time to get a good chunk of it read and edited. If I only work on a small part the book becomes very choppy. Even though I have written the whole book myself I sometimes forget what I have said and what I want to say further on. That is one reason why it is a good idea to have editors and other people to look at the book besides me they can catch what's not really written into the words on the page and help me decide how to make it clearer. Sometimes things are found to be in my mind, but not really written down. I need them in the book or the readers won't come to the same conclusion.
That's what I'm working on, making sure the book has cohesiveness and that no minor character, like the dogs get forgotten.