I wonder if the reason schoolkids are so fiercely competitive in popularity is because they have so little to distinguish themselves from others (fueled in egoism), and if the social/mental changes people undergo if/when they enter periods of their life (perhaps prison is a good example?) where their differences are partly shed can be understood as being significantly caused by this. As people age in school, that competitiveness fades as people legitimately come to differ from "the crowd" in the activities they choose and accomplishments they accumulate. Adult life adds entire new dimensions of difference, as people settle into a socioeconomic class, have positions in a company, and similar - they can more easily find ways to interpret their criteria of value in life to feel that they're better off than most people they know (and as there are so many potential criteria out there and deep information about other people becomes hard to find, there's room for most people to be "pretty good" or "the best" in what they care about, e.g. "I think I'm a just person who's a pretty good carpenter", or "I'm loyal to my friends, fuck the system, and I pull in enough money to support my family").
I'm not sure how devoted I am to this idea - it just crept into my mind. It has a certain intuitive strength though.