Yu Boya is good at playing the piano, and Zhong Ziqi is good at listening. When Yu Boya was playing the piano, he thought of mountains. Zhong Ziqi said, "Okay, I seem to see a towering Mount Tai standing in front of me!" Yu Boya thought of flowing water. Zhong Ziqi said, "Okay, I seem to see a galloping mountain. The endless river!" In short, Zhong Ziqi must know what Yu Boya is thinking. After Zhong Ziqi's death, Yu Boya felt that he no longer had a close friend in the world, and felt very sad. So he broke the piano, broke the strings, and decided not to play the piano again in his life.

This is the story of "Yu Boya dropped his zither to thank his close friend." Yu Boya missed his son Qi sadly, and people used this to lament that it was difficult to find a close friend.

Since then, because of this story, people have compared "mountains and flowing water" to a friend who is hard to find or a beautiful piece of music, and a "friend" to someone who understands one's own mind and has the same language as oneself. The word "Yijuexian" has gradually evolved into a meaning: to give up a certain expertise or hobby due to the death of a close friend, to express mourning.