I think that much of the narrative is devoted to this idea. Primo Levi himself said as much in an interview before his death when he said that the the primary motivation of the work was "“struggling to explain to others, and to myself, the events I had been involved in.” Levi's work is a treatise dedicated to understanding more about what it means to be a human being in the worst of all settings. What he is surrounded by represents "something terrible" and through this, Levi seeks to understand what it means to be a human being. He does not pass judgment, but the moments in which he understands that "there is no why here" or sees the death of a resistance fighter or even observes people around him doing whatever can be done in order to survive even at the cost of human contact might all represent "something terrible" that seeks to establish what it means to be human in the worst of conditions. There is not necessarily one particular bad specific moment where human nature is revealed to Levi. Rather, it is more of a collection of images in which how humans behave in the worst of conditions. Levi wishes to give voice to these experiences, reflecting how he seeks to understand more about human nature.