Each book I write, I struggle with this question. And I'm not alone. Even with many publications behind me, it's incredibly difficult to tell when a book is really done.
There is an end point. Truly. Part subjective, part objective. But it can be confusing or depressing en route to that place. One of my students recently questioned whether her book could ever be ready. "Some ideas may not be worth the effort or the money," she told me.