During the Spring and Autumn period, the state of Chu, seeking dominance over all feudal lords, expanded northward from the Yangtze River basin, subduing smaller states like Cao, Wei, Chen, and Cai along the Yellow River. However, the state of Song refused to ally with Chu and instead sided with Jin. Enraged, King Wei of Chu ordered his general Ziyu to lead an army against Song, quickly besieging its capital, Shangqiu.
Duke Cheng of Song urgently sought help from Duke Wen of Jin. Upon receiving the urgent message, Duke Wen of Jin summoned his minister Hu Yan to discuss the matter. Hu Yan said, "Sending troops to rescue Song will enhance Jin's prestige and lay the foundation for hegemony. We should dispatch troops."
Duke Wen of Jin said doubtfully, "The enemy is strong and we are weak; defeating them will likely be very difficult!"
"I have heard that those who value propriety do not tire of detail, and those skilled in warfare do not tire of deception. We can use deceitful methods—first find an excuse to attack Cao and Wei, then stir up Qin and Qi's discontent with Chu, making them send troops to join the battle. In this way, we will surely defeat the Chu army!"
Duke Wen of Jin had doubts about the strategy proposed by Hu Yan, so he summoned his advisor Yong Ji for counsel. Yong Ji opposed using deception, using a metaphor: "Imagine a man who wants to catch fish—he drains the pond completely, catching many fish, but the pond will have none left next time. Another man wants to hunt beasts—he burns down the entire forest, catching many animals, but the mountain will be barren afterward. Defeating enemies through deceit is like draining the pond to catch fish or burning the forest to hunt beasts—it may work temporarily, but it is never a long-term solution."
However, Yong Ji could not devise a better strategy, leaving Duke Wen of Jin with no choice but to adopt Hu Yan's plan.
Duke Wen of Jin immediately launched an attack, first striking the weaker states of Cao and Wei. Upon hearing the news, Zi Yu lifted the siege on Shangqiu and led his army north to rescue them. Thus, the Jin and Chu forces clashed at Chengpu. During the battle, the Jin army first crushed the right flank composed of Chen and Cai troops, then feigned a retreat to lure the Chu forces into pursuit, before launching a pincer attack that decisively routed the Chu army.
After the Battle of Chengpu, Duke Wen of Jin's reputation soared, making him the hegemon of the time. When rewarding his ministers, Duke Wen gave Yong Ji more rewards than Hu Yan. A close advisor, thinking the duke had made a mistake, asked, "Hu Yan contributed the most to this victory, so why is Yong Ji's reward greater than his?"
Duke Wen of Jin explained, "Yong Ji's words were a long-term plan; Hu Yan's strategy was an expedient measure. Therefore, Yong Ji deserves the greater reward!" Later, the idiom "draining the pond to catch the fish" came to describe seeking only immediate gains without considering long-term consequences.
Source: *Lüshi Chunqiu*, Chapter "Yi Shang"
Meaning of the Idiom: Later, the Chinese idiom "竭泽而渔" came to describe seeking only immediate gains without considering long-term consequences.