Yun, an ancient wind instrument.

"Playing the Yu just to make up the numbers" means that people who don't know how to play the Yu mix among the many musicians to make up the numbers. Excerpt from "Han Feizi." "On Internal Storage". Later, it was used as a metaphor for people who have no real talent and knowledge and mix themselves among experts to make up for their mistakes. It is also used as a metaphor to fill up the scene with bad things. It is also used to express self-effacement and to describe one's own lack of talent and virtue.

"Han Feizi. There is a story in "Nei Chu Shuo Shang": During the Warring States Period, King Xuan of Qi liked to listen to the Yu ensemble, so more than 300 musicians played together every time. There was a Mr. Nanguo who, although he could not play the Yu, knew about King Xuan of Qi's hobby, so he asked King Xuan of Qi to let him join the band, and King Xuan happily agreed. Whenever many musicians were playing together, Mr. Nan Guo would blend in with the hundreds of Yu players and pretend to be playing. No one would find out the truth, and he would get very good treatment. After the death of King Xuan, King Min succeeded to the throne. Although King Min also liked the sound of Yu playing, what he liked most was solo performance, so he ordered the musicians to perform in turn. Mr. Nanguo got the news and knew that he could no longer get away with it, so he had to escape from the palace. Later, this story was condensed into the phrase "fake tricks to show off", which is used to describe people who have no real talent and knowledge, but mix among experts to show off, or to use bad things to show off. Sometimes it is also used as a self-effacing expression to describe one's own lack of talent and virtue.