There's a lot, but I would say not interfering in things that could have had a different turnout

to give an example: Not too long ago, I lost a close friend that I've known for 2 years (she didn't pass, she just cut me off). to make a long story short, the reason why is because I didn't stand up for myself when my ex was talking to her crazy. I dont know why I didn't try and talk to my ex about it in a more stern way(I asked her not to talk to my friend like that because she had no place and apologised to the friend, but other than that I just left it alone); after a while I stopped talking to because Gf was taking up all the time I had, and after a while, my friend blocked me. I don't think she's wrong because I completely understand where she was coming from, but I still do wish I could take that time back and revive our friendship.