Yu Boya is good at playing the piano and Zhong Ziqi is good at listening. When Yu Boya played the piano, he thought of the mountain in his mind. Zhong Ziqi said, "Well, I seem to see a towering Mount Tai standing in front of my eyes!" Yu Boya thought of running water in his heart, and Zhong Ziqi said, "Well, I seem to see a rushing river!" In a word, Yu Boya thinks that Zhong Ziqi will know his mind. After Zhong Ziqi's death, Yu Boya felt very sad because there were no bosom friends in the world. So I broke the piano and the string, and decided not to play the piano all my life.

This is the story of "Yu Boya thanked his bosom friend with the piano". Yu Boya sadly missed his childhood, which made people sigh that bosom friends were hard to find.

From then on, because of this story, people compared "mountain stream" to a hard-to-find bosom friend, or a bosom friend with wonderful music, and compared "bosom friend" to a person who knows his own heart and has the same language with himself. The word "an excellent scholar" gradually evolved into a meaning: to give up a specialty or hobby because of the death of a bosom friend as a token of mourning.