--- Chinese saying (Google Translate)
Via ShinikenHarui in the comment section of the TwoSetViolin episode World Class Prodigy Violinist Chloe Chua Gives TwoSet a Violin Lesson, Sep 2020, translated as "there's always another mountain taller".
For a few more translations, see a page on Baidu ("天外有天，一山还比一山高" 的英语翻译). The full saying seems to be "天外有天，一山还比一山高”, "There is a sky outside the sky, and a mountain is higher than a mountain" (according to Google Translate)
