The author evaluates the possibility of the concept of pessimism establishing itself as a relevant factor within the theory of realism in international relations, that is, for explaining past and future events in international politics. The approach applies the meta theoric interpretative method in order to expose some of the tenets of the leading pessimistic theories where the focus is on classical realism within the realistic theory, since its origins are also the fundamental origins of pessimism. The first part exposes the fundamental postulates and essence of realism and pessimism, while the second part focuses on the intellectual background of the pessimism thought found in the works of Schopenhauer, Nietzsche and Freud. The last part expose a criticism of optimism as well as the fundamental contradictions in understanding the concept of time between pessimism and optimism, as well as the implications of pessimism on international relations. Pessimism, as a part of the theory of realism in international relations, has a philosophical force and a powerful theoretical background that gives it a place in the realistic theory of international relations.