Man, according to Schopenhauer, is driven by continued, unachievable desires, and the gulf between our desires and the possibility of achieving them leads to misery while the world is a representation of an unknowable reality. Our representation of the world is Phenomenon, while the unknowable reality is Noumenon: concepts originally posited by Kant. Schopenhauer's influence on "Tristan und Isolde" is most evident in the second and third acts. The second act, in which the lovers meet, and the third act, during which Tristan longs for release from the passions that torment him, have often proved puzzling to opera-goers unfamiliar with Schopenhauer's work.