When Emperor He of the Eastern Han Dynasty, Liu Zhao, ascended the throne, the Empress Dowager Dou held power, and her brother Dou Xian was appointed Grand General, with all major civil and military officials controlled by the Dou family, effectively sidelining the emperor and plunging the court into instability and chaos.
That same year, a solar eclipse occurred—a rare celestial event. Seizing the opportunity, someone submitted a secret memorial to the emperor, claiming this eclipse was an ominous sign of misfortune.
This man was the learned scholar and imperial advisor Ding Hong, who had mastered the classics. He said, "The sun represents the emperor, and the moon represents his ministers. A solar eclipse means the ministers are encroaching on the emperor's power." He then cited evidence: "Your Majesty, in the Spring and Autumn Annals, there were 36 solar eclipses, and 32 of them were followed by ministers killing their rulers. The cause is always the same: the emperor granted his ministers too much power, allowing them to act recklessly and eventually seize the throne."
Ding Hong also enumerated the crimes of Dou Xian and his brothers for overstepping their authority and usurping power. He warned, "If Your Majesty continues to neglect state affairs and indulges the Dou brothers, history will repeat itself. Moreover, Heaven has already sent us a warning—the Dou family's power now threatens the Liu imperial house! You must change this situation starting now: nip evil deeds in the bud by addressing small matters. If you do, calamities will be averted and blessings will follow."
Afterward, Emperor Liu Zhao decisively stripped Dou Xian and his associates of their official positions, and the Dou brothers were forced to commit suicide, thereby securing his own grip on power.
Later, the idiom "nipping in the bud" came to describe stopping mistakes or bad things at their earliest stage, preventing them from developing.
Source: *Book of the Later Han*, Chapter "Biography of Ding Hong"
Meaning of the Idiom: Later, the Chinese idiom "防微杜渐" came to describe stopping mistakes or bad things at their earliest stage, preventing them from developing.