Determine the maximum loss with which you are comfortable at the outset of an undertaking, be it a stock purchase or a new project.
Put your stop order in at the time you buy. It’s amazing how some efforts can dive. If you don’t know when to let go of a project, it can pull you under! It’s the classic Monkey Trap, never freeing yourself with your hand through the bars, around the banana you’ll never get.
Optimism can become a desperate hope that obscures. Be objective. If the project is going to fail, let it fail fast, freeing you to do something with greater odds of success.