I do it all the time - it's literally self-abuse! I'm not good enough, smart enough, pretty enough, rich enough, confident enough. I'm going to fail. Who am I to have such grand dreams? I made so many mistakes.
These are the stories that play through my mind every day. Sometimes I get on with things despite these stories. Other times these stories can really hold me back. After all, everything starts with a thought. If I think 'I'm not good enough', this has a snowball effect on how I feel and act, and ultimately the results I experience.