If the original poem says there is a piano sound, why not put it in the box? If the piano sounds from your hands, why can't you hear the sound?
Music with wonderful philosophy is an organic whole, which is composed of several parts and elements that influence and restrict each other. In music and piano sound, fingers, piano, players' thoughts and feelings, playing skills and other parts and elements are interdependent and indispensable, influencing and restricting each other, and there is a close relationship. According to materialist dialectics, the fundamental content of universal connection is the connection between the contradictory parties within things and between things.
So what this song reveals is the contradictory relationship between piano, fingers and piano sound. If the players are included, then the relationship between the players' thoughts, feelings and skills and the piano and fingers can be regarded as the relationship between the internal contradictions (internal causes) and external contradictions (external causes) of things. The former is the basis of music production, and the latter is the condition of music production, both of which are indispensable.