During the Warring States period, King Wei of Qi was so addicted to wine that he neglected state affairs, and in 371 BC, the state of Chu seized the opportunity to attack Qi. Unable to hold their ground, the Qi army sent the senior official Chunyu Kun to seek reinforcements from Zhao.
Chunyu Kun was less than seven feet tall, but he was eloquent and persuasive. He often went on diplomatic missions and never failed his mission. When he saw that the gift for the King of Zhao was only a hundred jin of gold, he couldn't help laughing heartily, even breaking the strap of his hat. King Wei asked him, "Why are you laughing, sir? Is it because you think the gift is too little?"
“No,” Chunyu Kun said, “Today, as I came from the east, I saw a farmer praying to the Heavenly Emperor with a cup of wine and a pig’s trotter, hoping for a bumper harvest so abundant that carts couldn’t hold it. I laughed at him for giving too little yet asking too much.”
King Wei, understanding his intent, increased the gifts to a thousand yi of gold, ten pairs of white jade discs, a hundred chariots, and four hundred horses.
Chunyu Kun arrived in the state of Zhao, presented gifts to the King of Zhao, who immediately agreed to send reinforcements to Qi and dispatched 100,000 elite troops to march day and night. Upon hearing this news, the King of Chu, fearing an attack from both sides, withdrew his forces overnight.
King Wei of Qi, delighted after repelling the Chu army, held a banquet in his inner palace and summoned Chunyu Kun to drink in celebration. He asked, "Sir, how much wine must you drink to get drunk?" "Your servant gets drunk with one dou and also with ten dou," Chunyu Kun replied wittily. "How is that?" the puzzled king asked.
When the Marquis of Wei asked Chunyu Kun about his drinking capacity, he replied, "In Your Majesty's presence, with officials standing guard, I tremble with fear and can barely finish one dou before getting drunk. But when elders visit my home, I must repeatedly urge them to drink, and I can manage two dou. When an old friend I haven't seen in years arrives, we share heartfelt stories, and I can drink five or six dou before feeling tipsy. At village gatherings, where men and women sit together without restraint, I can down seven or eight dou. But when night falls and my host keeps me alone for a private toast, my spirits soar, and I can drink an entire shi—ten dou."
Chunyu Kun continued, "Thus the ancients said, 'Excessive wine leads to chaos, excessive joy leads to sorrow.' Nothing should be overdone, or it will backfire."
King Wei of Qi, growing increasingly enlightened, resolved to abandon his drinking habit. From then on, Qi grew stronger day by day, reclaiming much lost territory. Chunyu Kun was appointed as the ceremonial officer for receiving envoys from other states.
Later, people used the idiom "Extreme Joy Begets Sorrow" to refer to excessive happiness that leads to sadness.
Source: *Zuo Zhuan*, "Biography of the Jesters"
Meaning of the Idiom: Later, the Chinese idiom "乐极生悲" came to describe excessive happiness that leads to sadness.