During the late Eastern Han Dynasty, as chaos engulfed the land and warlords clashed, Liu Bei, who had been garrisoned at Xiaopei, was defeated by Lü Bu and left without refuge. Forced to seek shelter, he temporarily submitted to Cao Cao. Delighted, Cao Cao hosted a grand banquet in his honor and appointed him Governor of Yuzhou.
After the banquet, one strategist warned Cao Cao, "Liu Bei is no ordinary man—if you don't kill him now, he will become a future threat." But another advisor, Guo Jia, countered, "This is a time when we need talent. Liu Bei is a hero; killing him would tarnish your reputation as a slayer of the worthy, harming your quest to unite the realm." Cao Cao agreed with Guo Jia's reasoning.
The following year, Yuan Shao's power in Jizhou grew increasingly formidable, while Yuan Shu, who had seized control of Huainan, planned to send the imperial jade seal he had secretly hoarded to Hebei, urging his elder brother Yuan Shao to declare himself emperor. Cao Cao, unwilling to see the two Yuan forces unite, prepared to dispatch troops to intercept. Seeing his chance to escape, Liu Bei told Cao Cao, "Yuan Shu's route to join Yuan Shao must pass through Xuzhou. Let me lead a force to intercept him there—I guarantee I can capture Yuan Shu."
Cao Cao had no doubts and, after reporting to Emperor Xian, allocated fifty thousand troops to Liu Bei. Liu Bei immediately set out with his army. Guan Yu and Zhang Fei, seeing Liu Bei's hurried demeanor, asked him in confusion, "Brother, why are you in such a rush for this campaign?"
"I am like a bird in a cage or a fish in a net under Cao Cao's command, unable to display my skills. This campaign is like a fish returning to the sea, no longer restrained."
Shortly after Liu Bei left, Cheng Yu and Guo Jia returned from their travels and, upon hearing the news, hurried to see Cao Cao.
Cheng Yu said, "When Liu Bei previously sought refuge, I begged you to kill him, but you did not listen. Now you have given him many troops—this is like releasing a dragon into the sea or letting a tiger return to the mountains! It will be very difficult to control him in the future."
Guo Jia also advised against allowing Liu Bei to lead troops on a military campaign.
Convinced by their reasoning, Cao Cao dispatched Xu Chu with troops to bring Liu Bei back. Liu Bei, naturally unwilling to return, defeated Yuan Shu near Xuzhou, took control of the city, and from then on broke away from Cao Cao to establish his own power base.
Later, people used the idiom "Releasing a Tiger Back to the Mountain" to describe letting an enemy return to their lair, leaving behind a source of trouble.
Source: *Romance of the Three Kingdoms*
Meaning of the Idiom: Later, the Chinese idiom "纵虎归山" came to describe letting an enemy return to their lair, leaving behind a source of trouble.