" The difference between international politics as it actually is and a rational theory derived from it is like the difference between a photograph and a painted portrait. The photograph shows everything that can be seen by the naked eye; the painted portrait does not show everything that can be seen by the naked eye, but it shows, or at least seeks to show, one thing that the naked eye cannot see: the human essence of the person portrayed...
Political realism presents the theoretical construct of a rational foreign policy which experience can never completely achieve.
At the same time political realism considers a rational foreign policy to be good foreign policy; for only a rational foreign policy minimizes risks and maximizes benefits and, hence, complies both with the moral precept of prudence and the political requirement of success. Political realism wants the photographic picture of the political world to resemble as much as possible its painted portrait. Aware of the inevitable gap between good—that is, rational—foreign policy and foreign policy as it actually is, political realism maintains not only that theory must focus upon the rational elements of political reality, but also that foreign policy ought to be rational in view of its own moral and practical purposes. "

― Hans J. Morgenthau , Politics Among Nations