The Nietzschean ressentiment (ray-sent-uh-mah) is the Existentialist concept of how an individual reacts to failure. Instead of dealing with the reality of inferiority or failure, one shifts one's values to match one's present state.
I must note that my life right now is rather not full of existential despair of any kind. However, much of the music I like has in it a sense of steady, impending doom and evil.
Now it is time to play guitar.