Status is the water in which we swim. Our social standing, how we stack up against others — these are primal, deeply buried motivators.
Our choice of others, on inspection, is bizarre. There's no rational reason why we should compare ourselves to old friends, past classmates, and so on. Especially in school, we're grouped together by random chance and measured against Procrustean beds. Nobody was on the same starting line or had the same childhood circumstances; our only inarguable commonality is that we shared the same physical spaces for a period of time. Yet we act as if these people (who often exit our lives post-grad) are the benchmark to determine whether we're superior or inferior, ahead or behind.
The same logic applies to our current communities. Why should you compare yourself to friends, coworkers, or acquaintances you met for an hour at a party one time? We're all standing here because of a dice roll, not a scientific study. And sharing similarities with someone fails to make you comparable at a holistic level.
Our neverending elbowing, glancing about, and whispering to figure out where we stand on the totem pole is so deeply wired that nobody questions it. We treat envy and jealousy as fundamental, when they actually seem to be second-order effects of our incessant self-comparisons with arbitrary people.