It was about four thousand years ago. Huangdi (Yellow Emperor)-the first legendary ruler in China went to the countryside to visit an old friend with his entourage. They met a boy keeping watch over a herd of horses on their way.

Huangdi asked the boy, "Do you know the way to my friend's village far away from here?"

The boy said yes.
Then the emperor asked, "Do you know my friend?"
The answer was yes again.
Huangdi thought the boy was broad-minded. So he asked him,"Do you know how to rule a country?"

The boy said, "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 left, brooding over the boy's words.
The idiom "The horse which does harm to the herd - A black sheep" is taken from what the boy said and is used to describe anyone who has a bad influence on his peers.

大约四千年前，黄帝－传说中中国的第一个帝王，带着随从去乡村看望他的一个老朋友。路上，他们遇到了一个看守马群的小男孩。

由于去朋友的村庄路途遥远，黄帝就问小男孩：“你知不知道村庄的路？那儿住着我的一个朋友。”
男孩说知道。

黄帝又问男孩：“认不认识我的朋友？”
男孩回答认识。
黄帝想这小孩懂这么多，于是问他：“你知道该怎样治理国家吗？”
男孩说：“治理国家的方法和看守一群马差不多。只要把野马从马群里赶出去就行了。”
黄帝离开时一直想着小男孩的话。

成语“害群之马”出自于这个小男孩说的话，用来形容给集体带来坏影响的人。

害群之马 (hài qún zhī mǎ)
【翻译】The Horse Which Does Harm To The Herd - A Black Sheep.
【释义】危害马群的劣马。比喻危害社会或集体的人。
【例句】他在公司散布很多谣言，是公司里的害群之马。
【近义词】城狐社鼠、残渣余孽
【反义词】仁人志士、谦谦君子