All people by nature are selfish. It is the desire for pleasure that drives all people. What an individual does is for their own pleasure - it may be that the pleasure is over time, or in the distant future, or may cause them more pain in the immediate sense but will ultimately cause pleasurable events.

If a person does something charitable, it is because the helping of other people gives that person pleasure. Others find pleasure in the domination of other people pleasurable. Some people find the concept of Paradise after death to be the ultimate pleasure; thus any sacrifices they have in this life are worth the ultimate pleasure of eternity. It is not necessary to believe in Paradise after death to do good things for others. Is not just the sight of a smile on another's face from one's actions worth it to some people? Is it necessary that there be some greater reward?

What is Good is that what allows for pleasure. Some people find pleasure living in a society. For them, that which preserves and enhances the society is Good and that which destroys it is not Good. Others find living their life in apart from others to do as they please giving them pleasure. To the later group, society is not Good, as it imposes constraints upon their actions. Some people take pleasure in creating, others in destroying. Some people take pleasure in advances of science; others despise its advances. To each individual, Good has a different meaning - who am I to say what is Good beyond my own pleasures?

Thus, each person's actions are for what they consider to be Good. This by no means, is a new idea.

No evil as such can be desirable, either by natural appetite or by conscious will. It is sought indirectly, namely because it is the consequence of some good.
--St. Thomas Aquinas, Summa Theologiae, I, Pt. 1a, qu. 19, a. 9

Every man, from the laws of his own nature, necessarily seeks or avoids what he judges to be good or evil.
--Baruch Spinoza, Ethics, Part 4, Proposition 19