A selection of my top few regrets:

• Getting into a relationship I didn't know how to get out of. (Result: I feel like years of my life have been wasted, and I was seriously distracted during an important period of my education.)

• Not learning to code in college. (Result: Hard to say at this point, but probably financially costly and I'd feel much better about myself if I'd graduated with a marketable skill. It's definitely easier to learn when there's some time pressure and also TAs who can help you figure things out.)

• Not taking advantage of moderately frightening opportunities that I thought would remain open for years but in fact closed within weeks. (Result: Details are personal, but I believe it contributed substantially to mistake #1.)