Today, it is a widely accepted theory that humans are largely motivated by self-interest, or things that are perceived to work in our favour. This theory of psychological egoism is largely attributed to Thomas Hobbes and Jeremy Bentham, but Bentham was born more than a hundred years after Hobbes, which generally speaking makes Hobbes the originator of this theory.
We can see this idea reflected in Hobbes’ Leviathan, but there isn’t really a specific argument for these views, it seems as if Hobbes just assumed that this was the nature of things. “For no man giveth but with intention of good to himself, because gift is voluntary, and of all voluntary acts the object is to every man his own good; of which, if men see they shall be frustrated, there will be no beginning of benevolence or trust; nor, consequently, of mutual help” (pg.95, l.15.16). He says that, but he never really expands on why that is.
Because of the lack of proof, this theory is not accepted by everyone, and many people believe in psychological altruism, the theory where humans have ultimately altruistic motives. If one holds this belief, then the egoist premise of Hobbes’ society falls apart. However, like psychological egoism, psychological altruism does not carry any concrete proof either.
In the end, it’s up to the reader to decide whether to believe in psychological egoism or altruism, and this greatly changes how one views Leviathan.