During the Spring and Autumn period, after Zhi Bo of the State of Jin destroyed the Fan family, a man took the opportunity to sneak into the Fan estate to steal. Upon entering the courtyard, he saw a large bell. It was beautifully designed and cast from high-quality bronze. The thief was delighted and decided to take it home.
However, the bell was too big and heavy to move. After much thought, he concluded he must break it into pieces to carry it away. He found a large iron hammer and struck the bell with all his might. The blow produced a loud, resonant crash that terrified him. In a panic, he threw himself onto the bell, trying to muffle the sound with his arms, but to no avail. The clear sound continued to travel far and wide.
The more he listened, the more frightened he became. He instinctively covered his ears with his hands. "Ah! The sound is fainter now, almost inaudible," he thought cheerfully. "How wonderful! Covering my ears blocks the sound." He immediately found some cloth, made two plugs, and stuffed his ears. Believing that no one could hear the bell now, he felt relieved and began striking it repeatedly.
The resounding noise, however, was heard in the distance. People followed the sound and caught the thief.
This story originates from "Knowing Yourself" in The Annals of Lü Buwei, compiled just before the Qin Dynasty (221–207 BC). It is said that when Emperor Gaozu of Tang (Li Yuan, reigned 618–907) read this story, he found it utterly ridiculous and remarked, "This is what is called plugging one's ears while stealing a bell."
Later, the idiom "plugging one's ears while stealing a bell" came to describe the foolishness of those who deceive themselves while trying to deceive others.