-Thinking I should follow advice I got from older respected people. The best advice I've ever had is that "lots of advice is BAD advice, or at least bad for you." I wanted to be open to criticism, and I'm into self-improvement, so I used to take advice really seriously when it came from a remotely intelligent source. Lots of it was contradictory, lots of it didn't apply to me and my specific situation and personality, lots of it arose from the special particularities of the advisor, and lots of it was just people saying vague things that sounded wise to feel like they had something to offer me. Instead, I started taking surprising/unusual advice (which really is the only useful kind, in my opinion) seriously only when it came from someone who knew me and my situation well, I understood the reasoning behind it, and I had gotten similar second opinions from other respected sources.

(Also, asking the advice of people I respected at a young age (12-19) instead of going online to find solid, well-tested, data-supported strategies to deal with my problems and questions).

-Doing research in a field that didn't interest me early on because I felt like I should be doing research of some kind, thought it would gain me prestige, and thought it would not be overly time-consuming. In reality, it probably did get me some limited prestige, but the opportunity cost was exorbitant. It was extremely time-consuming, and additionally added to feelings of stress, meaninglessness, and frustration at that time in my life.

-Not getting on okcupid for a long time because of the social stigma in my social circle. I've met so many amazing people on that site, including my current SO, plus it exposed me to a wider community, taught me what more people outside my community like/want/act like, and built my confidence about my ability to find love and romance if my current relationships fell through. This helped me become choosier (and thus more able to pick out smarter, kinder people I enjoyed more) and less anxious about dating in general (which made me a kinder, more fun person to be around).