From 《
列子·
汤问》: the qin master Boya played, his friend Zhong Ziqi said, 'How lofty — like Mount Tai!' Then, 'How vast — like rushing rivers!' When Ziqi died, Boya broke his qin, believing no one else could understand his music. Hence
高山流水 = deep, mutual understanding (
知音 zhīyīn).