What stuck in the minds of these men who had become murderers was simply the notion of being involved in something historic, grandiose, unique (“a great task that occurs once in two thousand years”), which must therefore be difficult to bear. This was important, because the murderers were not sadists or killers by nature; on the contrary, a systematic effort was made to weed out all those who derived physical pleasure from what they did. The troops of the Einsatzgruppen had been drafted from the Armed S.S., a military unit with hardly more crimes in its record than any ordinary unit of the German Army, and their commanders had been chosen by Heydrich from the S.S. élite with academic degrees. Hence the problem was how to overcome not so much their conscience as the animal pity by which all normal men are affected in the presence of physical suffering. The trick used by Himmler — who apparently was rather strongly afflicted by these instinctive reactions himself — was very simple and probably very effective; it consisted in turning these instincts around, as it were, in directing them toward the self. So that instead of saying: What horrible things I did to people!, the murderers would be able to say: What horrible things I had to watch in the pursuance of my duties, how heavily the task weighed upon my shoulders!

Hannah Arendt (1906-1975) German-American philosopher, political theorist
Eichmann in Jerusalem: A Report on the Banality of Evil, ch. 6 (1963)