Statesmen understand human nature. Why not psychologists and social scientists?
Most psychologists don’t like human nature, or at least not the idea of it. Clinicians, life coaches, and corporate motivators dislike it because it implies unchangeability. Anyone who took college psychology knows how to modify behavior, from direct instruction to manipulative advertising.
And then, what fool surveying the huge variety of human personalities, needs, and tastes would dream of trying to characterize all that as one thing? Well, some fool might, but not the philosophers, evolutionists, historians and political leaders who have long used the phrase. They’ve always meant something complex, varied, and big-but not limitless.