It seems to me that once a story starts to hit the 40 - 50 chapters range, you need to go ahead and start trying to wrap it up. If it can't be truly finished, then close it out as best you can and start Book II. What is it with all these stories that go on for 60, 80, 150 chapters? I don't mind long books. But you can reach a point where it's too long. 150 chapters is too long. Depending on the overall page/word-count of a book, I think 60 chapters could be too long. As an author, you need to show some discretion and learn when to shut it down.