During the Western Han Dynasty, Emperor Wu of Han sent Tang Meng as an envoy to the Yelang Kingdom to build the "Southwest Yi Road." After arriving in the Bashu region, Tang Meng failed to unite the local tribes, imposed heavy taxes, and even executed a tribal chief, sparking unrest among the various Bashu tribes. When Emperor Wu heard the news, he dispatched the poet-official Sima Xiangru to mediate and calm the people's hearts.
The Han dynasty poet Sima Xiangru drafted a proclamation titled "Exhorting Ba and Shu," explaining to the people of Ba and Shu that the actions of the official Tang Meng were not the emperor's decree, while also urging the populace to obey the commands of the Han court.
The proclamation stated: It is right to conscript laborers for road construction, but some, ignorant of national laws and decrees, panic, flee, and harm each other, which is wrong. Soldiers in battle should charge forward bravely, not hesitate, retreat, or turn to escape; even if wounded or killed in action, they should never look back.
After the proclamation was issued, Sima Xiangru spent time negotiating with the leaders of the Ba and Shu tribes, eventually winning their understanding, and the unrest sparked by Tang Meng finally subsided.
The idiom "yi bu fan gu" was later written as "yi wu fan gu," meaning that once a person decides to do something righteous, they should not hesitate or retreat.
Source: *Records of the Grand Historian*, "Biography of Sima Xiangru"
Meaning of the Idiom: Later, the Chinese idiom "义无反顾" came to describe how once a person decides to do something righteous, they should not hesitate or retreat.