, (traditional, Pinyin ban1 men2 nong4 fu3)?literally means brandishing an axe at Ban’s gate. People use it to describe someone who shows off his inferior talent or skill in front of an expert. Do not teach fish to swim is another way to put it

Ban, is an abbreviation of Lu Ban. He was a Chinese carpenter, engineer, inventor and contemporary of Mozi, born in the State of Lu. He is widely recognized as the patron Saint of Chinese builders and contractors. Lu Ban is notable for his achievements after he became a subject to the State of Chu.

  is about Lu Ban and a young carpenter. Once upon a time a young carpenter was standing in front of a red gate. Brandishing his axe, the young carpenter said that he could create all the things in the world with his axe. A passerby, dissatisfied with the young carpenter’s words, asked whether he could make a better door than the red one he was standing in front of. The carpenter confidently smiled. He told him that he was a student of Lu Ban and could automatically make a better one.

The crowd burst into laughter and told this brash young man that the red gate he was standing in front of was Lu Ban`s.

Now its meaning has changed with the passage of time. People today may use it as a form of self-abasement before an expert; they may say it in modesty. Sometimes, it is used to encourage others to try new things and break new ground instead of mechanically practicing by the rules.