IMHO: Everyone makes mistakes. But not everyone can learn from his/her mistakes. Some people just keep on repeating the same mistakes again and again. These are called LOSERS. Only a few can learn from other people's mistakes, and are able to seek victories from defeats. Those are WINNERS.
I am reminded of the clinical term used to describe the typical stages of the grieving process. For me, losing at trading can be as emotional as losing a physical object (or person). The letters are DABDA. Denial: this isn't happening to me (again). Anger: how could this happen, I should know better, what an idiot I am! Bargaining: maybe it was just a mistake, maybe they'll bust the trade (LOL). Depression: I lost again, I'm a failure, I need to quit trading and get a "real" job. Acceptance: I screwed up again, what can I learn from this, and how can I avoid repeating the same mistake? I am not always aware of this process as it is taking place, but usually see the stages in hindsight. When I suffer an especially tough loss, which does happen occasionally, I try to allow myself to go through this "grieving" process. As they say in AA, "This too shall pass."
I like this one: "A man is not finished when he is defeated. He is finished when he quits." -- Richard Nixon