I know my team is better than yours because…

You might say that that in-group bias isn’t necessarily a bad thing – after all, it’s what keeps us together with the ones that are closest to us. Except, it makes us think that all our problems are despite out efforts, while all their problems are because of their inability, which is a real problem once we try to talk to a person outside our in-group.

That’s why it is good to be reminded sometimes of how random group identities are anyway.

Cartoon by xkcd.
Thanks to lisa.

Update: You can find a good social psychological overview of “the rules that govern groups” here.