Opportunity cost is definitely one thing I had in mind. Other than that, my peers were committed to various things like fundraising for charitable organisations

Opportunity cost is definitely one thing I had in mind. Other than that, my peers were committed to various things like fundraising for charitable organisations, doing something good by serving people in one way or another, voluntarily taking up responsibilities or just becoming a more well-rounded person by spending their time doing various things instead of just one thing. While they all did that, I just stayed at home playing games instead and acted like the sole purpose of life was to enjoy myself which is something worth regretting (and happy I've made some progress since then).