birds of a feather flock together字面是说“一样羽毛的鸟儿会聚在一起”，对应到中文是“物以类聚，人以群分”。

【例句】
Birds of a feather flock together, and therefore they are such good friends.
物以类聚，所以他们能成为好朋友。

Don't be friends with bad boys. People think that birds of a feather flock together.
不要和坏孩子交朋友，人们认为物以类聚，人以群分。