I'd say alcohol too. I didn't drink in college, so I got a lot of questions about why not. I responded basically that I viewed it as not necessary and detrimental to reaching all of my goals - academic, financial, health, relationships, etc.

While I agree with this attitude, sometimes I love to set an "exploration coin toss experiment, in which I deliberately choose something against my agency

Ah, as an introvert alcohol definitely didn’t play a detrimental role in my relationships, quite the opposite actually, rather pivotal.

To be clear, I do think that drinking would've helped me to make more friends and meet more girls (some guys asked me, incredulously, how I would ever meet girls if not at a kegger). But I didn't think that it would help me to make friends with people who shared my worldview, or develop the kinds of relationships that I wanted.