During the Warring States period, a short, witty, and brilliantly eloquent man named Chunyu Kun served the King of Qi, who often sent him on diplomatic missions that he always completed successfully.
After King Wei of Qi died, King Xuan succeeded him. One day, King Xuan sought to recruit worthy talents and summoned Chunyu Kun, asking him to recommend candidates.
Chunyu Kun recommended seven talented individuals to King Xuan of Qi in a single day. The astonished king remarked, "I've heard that finding a worthy person is as rare as seeing them shoulder to shoulder across a thousand li, and a sage appearing once a century is like one following another in a line. Yet you've presented seven in one day—how can I believe they are all truly worthy?"
Chunyu Kun argued, "Your Majesty, your point is valid but incomplete. Birds of a feather flock together, and beasts of the same kind walk together. If you search for medicinal herbs like bupleurum and platycodon in marshes, you'll never find them—but on Mount Liangfu and Mount Gaoshu, you can cart them away by the wagonload. Why? Because like attracts like. As the saying goes, 'Things of a kind come together; people of a mind form a group.' If you consider me a worthy man, then seeking other worthies through me is like searching for platycodon on Mount Liangfu—easy. Beyond these seven, I can find you as many sages as you need." Source: *Records of the Grand Historian*, "Biography of Chunyu Kun"
King Xuan of Qi listened and smiled with conviction.
"The idiom 'Birds of a feather flock together' originally meant that things of the same kind always gather together. Later, it often came to be used as a metaphor for bad people colluding with each other."
Source: *Strategies of the Warring States*, Chapter "Strategies of Qi III"
Meaning of the Idiom: Later, the Chinese idiom "物以类聚" came to describe things of the same kind always gather together.