Regret:

• Not taking care of my health. Too much sitting in front of a computer, not enough walking around. Too much junk food.
• Not keeping track of people after leaving their immediate circle (team changes, company changes, leaving college, etc.). Literally every opportunity I've had has come from somebody I know, yet I've done a poor job of keeping a network socially. It's not that hard to chat with people every few months, but I didn't initially put enough effort into it.

Happy:

• For me specifically, staying at my first job for a long time was really good. It helped me grow, and the company was pretty good with salary increases.
• In contrast to my regret, I did a good job of making friends with teammates and getting along with people I work with the most.