Classical realism is renowned for the nuanced understanding of international relations without reducing it to a realm of intense power-political competitions for security. It bridges the gap between individuals and international politics by attributing state behaviors to human nature, an unchanging concept transcending time and space. This paper focuses on Thucydides and Machiavelli's assumptions about human nature and their respective views of morality. Through close interpretations of the History of the Peloponnesian War and the Prince of Thucydides and Machiavelli, the two originators of realist international relations traditions, this paper explores from where classical realism's pessimism and cynicism derive? Why classical realism possesses a tragic view of world politics? The conflict between morality and the practical necessity of state survival in international politics constitutes another enduring theme in the two books. Thucydides laments the irresolvable tensions between morality and compulsions resulting from "fear, glory and profits," the three paramount human drives. Likewise, the Prince embodies the most cynical assumptions about the universal wickedness of human nature and the resulting tragic divergence between international politics and morality. Therefore, this paper argues that classical realism's cynicism and pessimism should not be taken for granted. Instead, they have historical roots in Thucydides' moral skepticism and Machiavelli's assumption about the prince's "wicked subjects." The cynical theory is an outgrowth and embodiment of the wicked men.