The 17th century philosopher Thomas Hobbes was one person who may have endorsed psychological egoism.
He wrote: “of the voluntary acts of every man, the object is some good to himself". But many philosophers – indeed most! – have rejected this theory. They are often moved by real world examples, such as soldiers who dive on grenades to save the lives of their fellows, or others who perform acts of apparent self-sacrifice such as organ donors and philanthropists.
1. Perhaps they convince you to change your mind, and instead claim that psychological egoism is wholly false.
2. Alternatively, you might claim that such acts are nonetheless chosen for self-interested reasons: these figures behaved in the way that they did in order to avoid a life of guilt, or behaved in the way that they did in order to achieve fuzzy feelings of reward.
3. Finally, you might claim that altruism, though possible, is nonetheless extremely rare: cases like those above might strike you as the exception rather than the rule.