I assume that people come to the gambling industry as inexperienced people. And in the process of their activities, they gradually learn from their mistakes. Unfortunately, some of these mistakes are dramatic and cause us quite serious psychological trauma. As a rule, this is due to gross errors and stupid persistent beliefs that push us to the edge of the financial abyss.

First of all, this is risk management and money management. The second is probably unsystematic play. Let me make a reservation that I do not mean casinos, as well as people playing "for fun".
So, how much did your mistakes cost? Did they cause you a serious psychological blow? What were your mistakes, did you learn from these mistakes and do you apply this knowledge in practice now? Were these mistakes simply painful, dramatic or catastrophic?