The horse that harms the herd
Refers to a person that has a negative influence on the group that they're in
Negative
这位恶徒总是经常打架闹事，真是社会的害群之马 | Zhè wèi è'tú zǒng shì jīngcháng dǎjià nàoshì, zhēnshi shèhuì de hàiqúnzhīmǎ
This vile person is always stirring up trouble. They're really a rotten apple in our society
[Source]
警界的腐败不止是几个害群之马而已 | Jǐngjiè de fǔbài bùzhǐ shì jǐ gè hàiqúnzhīmǎ éryǐ
Police corruption is not limited to a few rotten apples
[Source]
Rotten apple
None
The Yellow Emperor (黄帝, huáng dì) is a mythological ruler of China who lived over 4,000 years ago. He is also regarded as the ancestor of the Chinese people. (Be careful not to confuse 黄帝 with 皇帝 (huáng dì, or the generic title "emperor")
《庄子》(Zhuāng Zǐ), a work written by 庄子 (Zhuāng Zǐ, the same as in the title) during the Warring States Period (475 - 221 BC)
In ancient times, the Yellow Emperor (黄帝, huáng dì) was headed to visit a god. On the way, he happened to run into a child who was tending to horses in the field.
"Do you know the way to Juci Mountain?" called the emperor.
The boy replied that he did.
The emperor suddenly got the feeling that there was more to the boy than met the eye, so he asked him how to govern mankind.
The boy simply replied that governing mankind was like governing his herd of horses: if you didn't make trouble out of nothing and you got rid of the horses that caused trouble, everything would go smoothly.
The emperor was inspired, and he kowtowed repeatedly to show his gratitude for the boy's heavenly knowledge.