杜渐防萌 — “To nip evil in the bud”

During the reign of Emperor He of the Eastern Han Dynasty, there was a high-ranking official named Ding Hong. He was extensively well-read, eloquent, and courageous enough to speak out for justice, earning him great respect. At that time, Empress Dowager Dou presided over the imperial court, and her relatives, relying on their power, committed many misdeeds.

Ding Hong enumerated their crimes before Emperor He and carefully weighed the advantages and disadvantages. He believed that it was relatively easy to stop things when they first began to change, but it would become much more difficult later. If one did not pay attention to subtle changes in handling matters and allowed them to develop unchecked, it would be very hard to control the situation. He also suggested to Emperor He that he should personally manage state affairs and nip evils in their initial stages, thus averting disaster and bringing good fortune.

Emperor He quickly adopted Ding Hong's advice, eliminated these corrupt relatives, and personally took control of the government. The meaning of this idiom refers to preventing potential troubles before they arise. It is also used interchangeably with '防微杜渐' (fáng wēi dù jiàn), which also means to nip evil in the bud.