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". I mean sports betting.
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?
Well for me I don't think I will call mine a mistake but I guess it is still a mistake that actually cost me some money at first but I later learned and understand that gambling should not be approached in that manner and it's better you believe and trust your instincts.
At some point in gambling I thought it was better to follow games dropped by others in some groups, I believed they were experts and they are better at analysing games and picking odds in sports bets and that I was better off playing their games but in the end I lost more money than my winnings and mostly their games are for those who have high staking power. I later realized that it's better for me to analyze games myself and ever since I am more interested in my own games.
My mistake wasn't really painful but it's was an experienced I have learned from.