During the Eastern Han Dynasty, there was a talented official named Zhang Kan, who was skilled in both civil and military affairs. Orphaned at a young age, he generously gave away the millions of coins his father had left to his nephew.
When Zhang Kan went to Chang'an to study at sixteen, he was called a "saintly child" for his excellent character and learning. Emperor Guangwu of Han, Liu Xiu, greatly admired Zhang Kan even when his own status was low. Later, after becoming emperor, Liu Xiu promoted Zhang Kan and appointed him Governor of Shu Commandery.
At the time, Gongsun Shu, a former governor of Shu Commandery, declared himself emperor in Shu. Emperor Liu Xiu ordered Grand Marshal Wu Han to lead an army to suppress him. But Gongsun Shu held out in Chengdu, and the Han army, unable to breach the city for a long time, ran low on supplies. Wu Han was about to retreat. When Zhang Kan learned of this, he devised a plan: he had the soldiers pretend to be starving and challenge Gongsun Shu to battle. Gongsun Shu took the bait and personally led his troops out. To his surprise, the Han soldiers fought with extraordinary ferocity. Gongsun Shu suffered a crushing defeat and was killed at the gates of Chengdu.
After Zhang Kan entered the city with the Han army, he immediately inventoried the treasures in the government treasury, recorded them in official registers, and stabilized the populace, ensuring the people of Shu Commandery could live and work in peace.
Two years later, Zhang Kan was reassigned as the Governor of Yuyang, where he governed with clear rewards and punishments, never tolerating or indulging those who committed crimes, earning deep affection from the people.
Once, when the Xiongnu from the northern border launched a raid with ten thousand cavalry against Yuyang, Zhang Kan personally led his own horsemen to meet them, routing the enemy so thoroughly they fled in defeat. From that day on, the Xiongnu dared not invade again, and the borderlands enjoyed lasting peace.
Zhang Kan took advantage of the stable environment to extensively reclaim rice paddies around Yuyang, encouraging the people to farm diligently. After several years of hard work, the crops grew lush, products were abundant, and the people became prosperous. The local elders specially composed a song to praise Zhang Kan's governance:
"Mulberries without extra branches, wheat with double heads. With Lord Zhang in charge, joy knows no bounds."
The meaning is: the mulberry trees are pruned neatly with no extra branches; the wheat ears grow full, each ear like two. Lord Zhang governs here, and the people are overjoyed.
Later, people used the idiom "Overwhelmed with Joy" to describe being extremely happy.
Source: *Book of the Later Han*, "Biography of Zhang Kan"
Meaning of the Idiom: Later, the Chinese idiom "乐不可支" came to describe being extremely happy.