European philosophers: Friedrich Nietzsche, Martin Heidegger and Jean-Paul Sartre. The theme revolves heavily around the school of philosophical thought known as Existentialism, although the term had not been coined at the time of Nietzsche's writing and Heidegger declaimed the label. The documentary is named after the 1878 book written by Nietzsche, titled Human, All Too Human: A Book for Free Spirits.