What prevents people from understanding the events that occurred at Auschwitz, according to the author?

The correct answer is that the horrors are outside their realm of knowledge and experience. Crimes based on racism against the Jews and other ethnic groups at that time are hard to understand, because they were being executed just because of their belonging to a certain ethnic group. People were not clear about why where Jews guilty in the first place. A whole other realm is the way they were being executed, which is hard to comprehend no matter how we look at it. Concentration camps were places of extreme suffering that no normal human being would pose on another.