Although having regrets won't change anything but as humans there are some certain things that we will always feel. We have all dealt with losses, mine was on casino games and my only regret is knowing casino betting. My losses were a bit minimal on sports betting till I played casino games for a while. Regretting isn't going to change the past but you can definitely do something to fix the present.
I believe every human has certain things they once did, and lost money, which hurt them whenever they look back now.
However, I have never felt bad about losing money as a gambler because I already understand what is involved, and I know it's a game of chance which winning is not guaranteed, before I dive into it. The only thing I put money in and have regret in it whenever I look back is crypto ROI ponzi scheme back in my early crypto journey, before I later understood the concept is to scam their users.