A little late to the party, but my biggest regret is not making choices earlier in life. Always had many interests. In high school I did many extra extracurricular activities, I was programming at a local software company, I played piano in a band, I took guitar lessons because wanted to be a rock guitarist, started 3 studies in university, etc etc. It caused a lot of stress, and I never was really good at any of these.

Everyone always says you have to think about your what you want to do in life, but equally important is what not to spend time on. You can't have it all. If you want everything you end up with nothing.

Although I'm doing fine at the moment I see old friend having advanced further in their careers, due to focus, less stress and becoming really good at something. I kind of regret not giving my life direction in the past, choosing something and go for it.