Behind the public interest lies, in fact, a less altruistic aspect: the public usage of the private interest. Declaratively, a business man, a politician or an opinion maker won’t be followed in the acivities he undertakes if he admits that the reason behind his decisions consists in his own interest. It’s much more simple for him to hide his private interest behind a statement without foundation and practical aplicability, so as his decisions could be based on grounds that take into consideration factors that are different from his own person. The inexistence of the public interest does not imply that people make selfish decisions, self-orientated ones and it does not reveal a cruel world, devoided of altruism, civic spirit and morality. This article explains the fact that the public interest doesn’t have practical aplicability, from a conceptual point of view, and it defines each person’s activities in rational-marginal terms of cost-benefit.This way, each of us will take into consideration fundamental (moral, legal, academical) principles and personal experiences in order to evaluate the costs and the benefits of each action. Being aware of these facts and acting in accordance with these principles are the only ones that can lead to the achievement of that “general well-being” that can be achieved only when every individual acts in order to satisfy his own interest and pursues his personal goals.