Take gains and losses with the same indifferent reaction. Why are you worried at all at the possible downturn of anything? Your paranoia will only serve to make a poor outcome more likely. If a book succeeds and sells hundreds of thousands of copies, you shouldn’t react whatsoever. Think Bill Belichick.
This prevents you from having to react if you don’t sell hundreds of thousands of copies (because you won’t). Even better, it prevents you from being a downer if success is ever taken from you through force or sheer unluckiness. If you at any point allow your desire to be strong, you lose leverage because what you desire can be taken from you.