Self-doubt is the first step in keeping us sane and grounded. It is what brings the best in us, it makes us look over our plans with fine comb and it forces us to look at the bigger picture without losing sight of task at hand. I am in the same boat as you and find different things to worry about but I think it is better to worry when you still have the chance to make a difference rather than saying, “only if” at the end. I’m sure even when you launch your next book, you still will be worried.