The chief effort of this work is to face the implications for personal action of a universe without purpose. That man is personally responsible for what he is and what he does; that there are no values external to man and no given human nature which he is obliged to fulfill; that man chooses his values and makes himself, and may therefore choose to be a different person - this is the heart of Jean-Paul Sartre's philosophy. Annotation That man is personally responsible for what he is and what he does; that there is no given human nature which he is obliged to fulfill--this is the heart of Sartre's philosophy as explained here.