There are domains in which expertise is not possible. Stock picking is a good example. And in long-term political strategic forecasting, it's been shown that experts are just not better than a dice-throwing monkey.
Usually when I finish the draft of a book, I'm sure I'll never write another one. I'm just that tired and sick of myself. But then another idea starts percolating. It usually begins with the narrator's name, then some idea that intrigues me about her life or situation. I try to ignore it as long as I can, because I know when I start writing, I'll be right back into it, every single day. But eventually, I just have to. It's a compulsion!