She controversially uses the phrase 'the banality of evil' to characterize Eichmann's actions as a member of the Nazi regime, in particular his role as chief architect and executioner of Hitler's genocidal 'final solution' (Endlosung) for the 'Jewish problem'. Her characterization of these actions, so obscene in their nature and consequences, as 'banal' is not meant to position them as workaday. Rather it is meant to contest the prevalent depictions of the Nazi's inexplicable atrocities as having emanated from a malevolent will to do evil, a delight in murder. As far as Arendt could discern, Eichmann came to his willing involvement with the program of genocide through a failure or absence of the faculties of sound thinking and judgement. From Eichmann's trial in Jerusalem (where he had been brought after Israeli agents found him in hiding in Argentina), Arendt concluded that far from exhibiting a malevolent hatred of Jews which could have accounted psychologically for his participation in the Holocaust, Eichmann was an utterly innocuous individual. He operated unthinkingly, following orders, efficiently carrying them out, with no consideration of their effects upon those he targeted. The human dimension of these activities were not entertained, so the extermination of the Jews became indistinguishable from any other bureaucratically assigned and discharged responsibility for Eichmann and his cohorts.

Arendt concluded that Eichmann was constitutively incapable of exercising the kind of judgement that would have made his victims' suffering real or apparent for him. It was not the presence of hatred that enabled Eichmann to perpetrate the genocide, but the absence of the imaginative capacities that would have made the human and moral dimensions of his activities tangible for him. Eichmann failed to exercise his capacity of thinking, of having an internal dialogue with himself, which would have permitted self-awareness of the evil nature of his deeds. This amounted to a failure to use self-reflection as a basis for judgement, the faculty that would have required Eichmann to exercise his imagination so as to contemplate the nature of his deeds from the experiential standpoint of his victims. This connection between the complicity with political evil and the failure of thinking and judgement inspired the last phase of Arendt's work, which sought to explicate the nature of these faculties and their constitutive role for politically and morally responsible choices.