Aristotle believed that happiness was central purpose of human life and a goal in itself. That is, happiness depends on the cultivation of individual virtues, including physical as well as mental well-being. He argued that virtue is achieved by maintaining the Mean, which is the balance between two excesses.
Aristotle is a main advocate of egoism. He believed that for humans to be happy and to flourish, human beings ought to cultivate their self-interest. For Aristotle, every man is an end in himself and not a means to an end for others. Going against the belief of altruism (that morality consists in living for others or society), Aristotle believes that man must live for his own sake, neither sacrificing himself to others nor sacrificing others to himself (going back to man being an end in himself, not a means). Man must work for his rational self.
I think Arostotle was proposing a more self-centered approach to life than Epicurus. The latter put much more emphasis upon toleration and friendship. To him society had to hang together, or its constituent parts would hang separately. The influence here was the roiling wars that touched the lives of so many Greeks of his era. Be moderate, he said, seek happiness, yes, but self-interest had to be tempered with coperation, compromise and an understanding of other people’s motivations and interests. We need a message like this to go out, particularly to the divided American people or, yes, we’ll all hang together.