Has anyone ever wondered why we can't/refuse to be friends with someone who we are in indirect competition with? Ex: Two actresses as friends, two girls in general, two striving football players going for the same spot, etc.
We all do it. You may think you don't but you do. Two people who should by all rights be friends- same mutual friends, same interests, cool people- you end up resenting them for being successful OR more successful than you. You get the "Why them and not me?" mindset.
It's the reason why girls talk behind each others backs, why girls get a bad rap for being bad friends, why guys get into fights, why you don't get along with someone but you don't know why, why you secretly are jealous of someone else - Indirect competition creates resentment. It's true, we've all been there. You may be happy for the other person, but inside it's "why not me".