Second, to see self-interest from the nature of animals. So it's a scientific fact that people is inherently evil in the beginning. The beginning of man is the animal stage, isn't it?

Third, to see the contradiction between the benefits and righteousness. Thomas Hobbes said that human beings are like wolves, social life is the war against all human beings. The Chinese ancient philosopher Xunzi said, “Human nature is evil, those kind acts are acquired behavior.”

Fourth, to see people need restraint. Mencius was right when he advocated that one should lay down one's life for justice, but it was getting reactionary when Zhu Xi put forward the idea of “Knowing the truth, exterminating the desires.” The correct approach is to restrain and admit self-interest as justice.

Fifth, to recognize that personal gain is justice. Epicurus said: “A happy life is our highest supreme kindness.” He believes that wisdom, restraint, courage and justice are necessary only as a means of their own happiness.Confucius did not regard desire as the source of all evil. “When the national politics is clear, it is shame that some people are still poor and their status are low and humble.” Sima Qian said: “Everyone flocks for the benefit, also drift apart for it.” The recognition of the legitimacy of self-interest is an improvement, but it's not enough.

Six, to see the unity of profit and justice. Adam Smith, the father of economics, said: “Our dinner is not from the favor of chefs and butchers, but doing this way is good for them. The market system ensures that businessmen increase social benefits while maximizing their own interests, and the effect is better than when the traders take the initiative to do it.” 

Seventh, to see the importance of self-interest for the evolution of society. Humanitarianism and liberalism which rising from the beginning of the Renaissance promote the liberation of humanity. Marx believes that the economic foundation determines the superstructure