 So people made friends with the ones who were nearby them. And so this went into all the textbooks as, oh, just being exposed to someone, being regular contact produces friendship. But then 20 years later, somebody did a follow-up and also measured who became enemies. And it turns out living near somebody increases the likelihood you'll become enemies even stronger than the likelihood you'll become friends. Bellmeister found another example, a personal example, in parenting.