Boya's Solitary String tells a story that a bosom friend is hard to find. Yu Boya and Zhong Ziqi are a pair of good friends who have been sung for a long time. Yu Boya is good at playing and Zhong Ziqi is good at appreciating. This is the origin of the word "confidant". After Zhong Ziqi died, Yu Boya was heartbroken. He thought his bosom friend was dead, and no one in the world could understand the artistic conception of his performance like Zhong Ziqi. So, I broke my piano and never played it again. Because of this legend, people call people who really know themselves "bosom friends", and use "high mountains and flowing water" as a metaphor for hard-to-find bosom friends or wonderful music. After Boya, it is the extended meaning of "bosom friend", that is, close friend.