Those who wield great influence on humanity unfailingly understand some truth about the nature of human collectives. It could not be otherwise. They are able to hold power over the masses because they know — consciously or not — how to manipulate them.
Every individual is unique. Any and all of his mental and physical attributes may lie anywhere along the spectrum of human variations, not duplicated in its entirety in any other person. The individual person is idiosyncratic and unpredictable in his actions. But the masses behave entirely predictably. Humans are rational but only boundedly so. Psychologists who study group behavior have identified biases and systematic deviations from rational behavior. Those who rule the masses have necessarily to be experts in mass psychology.