人们往往因为兴趣、爱好、性格相互融洽而成为朋友，有的是志同道合，有的是臭味相投。

“物以类聚，人以群分”，中文俗语，比喻同类的东西常聚在一起，合得来的人相聚成群，是朋友之间志同道合的统称，可分开使用。与英文习语“birds of a feather flock together”意思相近，表示“People who have similar interests, ideas, or characteristics tend to seek out or associate with one another”。

例句：

乔治：你为什么认为唐纳德靠不住？

George: Why do you think Donald is dishonest?

内德：他的朋友都靠不住。物以类聚，人以群分。

Ned: All his friends are dishonest. Birds of a feather flock together.

我一直认为艾米很狂，而现在她和那个势利的男孩路易斯在约会。真是物以类聚。

I always thought Amy was pretentious, and now she's going out with that snobbish boy, Louis. Birds of a feather flock together.