I don't have any regrets. Honestly. At least I can't think of any. There are plenty of things, decisions, boys, and haircuts I would probably skip if I had the chance to go over and do it all again, but I don't really think regret is useful. I learned something from all of those things. Like that I hate when I have to actually do my hair every day or that boys who say "I don't like tequila or sports and I think we shouldn't tell anyone we're dating" are in the bad decision category.
On the flip side, I am all about Hakuna Matta, or YOLO to you youngsters. I like to [pretend to] not worry too much. Okay. That's not true, I'm a worrier. I know it's like chewing bubblegum to solve an algebra problem. BUT STILL. I use it as a motivational saying when I am on the fence about what I should do. Like that whole Europe trip? Yeah, that was a "if I don't do this, I'll hate myself" situation for sure. Not hate myself, but I'll always wonder "what if I had gone to Europe before I really settled down? Where would my life be now?" I don't ever want to wonder "what if" if I can help it.
So yes, I think regret is a waste of your energy and I think it's negative energy that can be better turned into "what did I learn from this situation? how can this help me in the future? what can I do better next time?" Next time you think you regret something, give yourself some constructive criticism instead. You're doing the best you can, so go easy on yourself.