A Rotten Horse Spoils the Herd 害群之马

The Chinese idiom 害群之马 (hai4 qun2 zhi1 ma3) literally means the horse which does harm to the herd. The idiom comes from a story about the Yellow Emperor (Huangdi), the legendary first ruler of China.

about four thousand years ago, Huangdi went to the countryside to visit an old friend with his entourage. On their travels they met a boy keeping watch over a herd of horses. Huangdi stopped to ask the boy for directions to the village wher his friend lived. The boy knew the village and provided the Emperor with directions. The Emperor then aksed the boy about a number other things. When the boy was able to help with these things as well, the Emperor formed the view that the boy was actually quite bright (intelligent). So he said,

You seem to be quite knowledgeable. I wonder, do you know how to rule an entire country?

The boy had a simple answer based on his experience herding horses,

Your Highness, there is little difference between ruling a country and watching over a herd of horses. You simply have to drive the wild horses out of the herd.

The Emperor found this refreshingly simple answer quite compelling. He thanked the boy and bid him farewell. The boy's words stuck in the Emperor's mind and he continued to mull over them for many days to come.

The boy's advice has become encapsulated in the Chinese idiom 害群之马 (hai4 qun2 zhi1 ma3). Today, Chinese people use this idiom to describe anyone who has a bad influence on his peers or disrupts the effective functioning of a group.

English speakers would describe this type of person as a bad egg or a rotten apple. The latter expression is actually a shortening of the proverb a rotten apple spoils the barrel. The idea here is that mould or other diseases in one apple will gradually spread to the rest of the apples in the same barrel, thereby ruining the whole barrel.

As a final point, it is worth noting that while the English idiom a black sheep has similar connotations about someone's character, that idiom more aptly applies to family situations. A black sheep is someone who is considered by others to have caused his or her family embarrassment or shame. It is more akin to the Chinese idiom 败家子 (bai4 jia1 zi3).