To put it in a more understandable way, it is called "the banality of evil." I think the meaning is: "evil" is hidden in what one considers to be "ordinary behavior." I heard an example: No drop of rain would think that it caused a flood. When a chain of evil deeds is long enough that people who are involved in every link of the chain cannot see the whole chain, everyone in the chain seems to have reason to feel innocent. Ordinary person A is just the clerk who registers the race of the Jews. B, a police officer who was ordered to escort Jews from their homes to a segregated area. C. The conductor who put the Jews on the train. Ding, the security guard who maintained order in the concentration camp. E, the cleaners responsible for collecting the corpses...why should they be held responsible for the deaths of these people? They are just small screws in a huge machine. But is Hitler alone responsible? 6 million, if he kills one person a day, it will take him more than 10,000 years to kill.

After reading the above examples, you should probably understand what "the banality of evil" means. "Evil" is a machine that produces destructive properties, and this machine is made of hundreds of parts. It only requires one button to operate it, but the operation of a machine is more than just pressing a switch! It also requires the cooperation of the internal parts of the machine, and often these parts don't think they are doing evil. They think I am just obeying the orders of my superiors. So evil is hidden in what they think are ordinary behaviors. These people only think that they are small screws, parts, and gears. In fact, they are all doing evil because they are all accomplices!