During the Spring and Autumn period, a scandal erupted in the state of Jin when two retainers of the minister Qi Ying, named Qi Sheng and Wu Zang, exchanged wives. Qi Ying, deeming this a private family matter unrelated to state affairs, arrested and executed the pair without reporting to Duke Qing of Jin.
When Duke Qing of Jin learned of this, he was already worried about Qi Ying's excessive power, so he used Qi Ying's private execution of a retainer as a pretext to have Qi Ying killed. At the same time, he declared the Yangshe clan to be Qi Ying's accomplices and had them executed as well.
In the autumn of that year, when the Jin state's chief minister Han Xianzi died, his successor Wei Xianzi took power. Wei divided the Qi clan's lands into seven counties and the Yangshe clan's lands into three, appointing capable officials to govern them. Among these appointees was Wei Wu, a man of the same clan as Wei Xianzi himself.
One time, Wei Xianzi met the official Cheng and asked him, "If I appoint Wei Wu to govern Gengyang, will people say I am biased, favoring him, and forming a faction?"
Cheng replied, "How can you call this forming a faction? Wei Wu is utterly loyal to our ruler, humble toward his colleagues, upright in character, and efficient in handling affairs—what's wrong with making him a district magistrate? When promoting officials, we should treat everyone equally regardless of personal ties: we must see if they can restrain themselves with moral principles, if they can teach others tirelessly, if they can be selfless and aboveboard, if they can reward and punish fairly, and if they can follow what is good. In other words, we must judge whether they possess both virtue and talent. As long as someone truly meets these criteria, there's no need to fear what others might say."
“You are absolutely right!” Wei Xianzi said joyfully. He then confidently sent Wei Wu to take up his post. Later, the idiom “Choose the Good and Follow It” came to mean selecting what is good and following it, whether referring to people or matters.
Source: *The Analects*, Chapter "Shu Er"
Meaning of the Idiom: Later, the Chinese idiom "择善而从" came to describe how selecting what is good and following it, whether referring to people or matters.