In ancient times, a young man named Zhu Hanman heard that Zhi Liyi was a master butcher of great renown, so he left his wife and children to seek him out and learn the art of slaughter.
After much difficulty, he found Zhi Liyi's home and asked to become his disciple. Seeing his sincerity, Zhi Liyi gladly accepted him and asked,
"Are you looking to learn the art of butchering cattle and horses, or the skill of slaughtering pigs and dogs?" Zhu Hanman thought to himself, "Butchering cattle, horses, pigs, and dogs is too ordinary; there are very few people in the world who know how to slay dragons—I'd rather learn the art of dragon-slaying." So he said to Zhi Liyi, "I want to learn the art of dragon-slaying." Zhi Liyi replied, "Dragon-slaying is no easy skill to master; you must study diligently for three years before you can achieve anything." Zhu Hanman responded, "Master, I can endure hardship and will surely succeed." Zhi Liyi added, "The tuition for learning dragon-slaying is also very steep—about a thousand taels of silver over three years." Zhu Hanman declared, "I am willing to sell off my family property to scrape together a thousand taels of silver for the tuition."
Thus, Zhi Liyi began teaching Zhu Hanman the art of dragon-slaying. Zhu Hanman studied with great diligence, repeatedly practicing the techniques his master taught him, and made rapid progress.
In the blink of an eye, three years passed. Under the careful guidance of his master, Zhili Yi, Zhu Hanman mastered the complete art of dragon-slaying.
After bidding farewell to his teacher Zhili Yi, Zhu Hanman returned home. Yet year after year, his dragon-slaying skills found no opportunity to be used—no one could even capture a dragon, let alone slay one.
Later, people used "the skill of slaying dragons" to refer to techniques that are highly advanced but utterly useless in practice.
Source: *Zhuangzi*, "Lie Yukou"
Meaning of the Idiom: Later, the Chinese idiom "屠龙之技" came to describe how techniques that are highly advanced but utterly useless in practice.