Human, All Too Human reflects upon the experiential side of belonging to the human collective. Nietzsche focuses in on our inherent need of explaining that experiential side of existence and Existence. It is our inherent need to create and/or support a transcendent structural framework to house our explanations or functionality of a given experience that motivates Nietzsche break down our defensive walls.
Nietzsche is often erroneously identified as a Nihilist. This point is arguable. In Human, All Too Human, Nietzsche labors endlessly to have you, the reader, experience a moment of clarity, to break through that sheltered Self and to bare witness to a life without assumption. Our individual human experience is always seen through the filters of our institutions whether it is science, religion, philosophy, etc. That is why we are "Human, All too Human".
The Nietzschean ubermensch is one who is not more highly evolved than others, but one who can understand the experiential side of life without the hue of institutions to color one's perception and eventual understanding.