When I was taking Philosophy 101 my professor made a remark that had a strong and lasting impact on my life. He said simply, "We are all selfish. "Yeah, right," I thought. "Jesus was selfish. Gandhi was selfish. Martin Luthor King Jr. was selfish."
But I continued to think about it, trying to understand what he meant, because he obviously couldn't have meant it at the face value. And as I thought about it, it gradually became clear. I never discussed this with the professor, so I don't know if the interpretation I came to is what he meant, but I decided he was right. We are all selfish.
This isn't selfishness as most of us interpret it, though. It is positive selfishness. Free Dictionary defines selfish as "Concerned chiefly or only with oneself". "How can that be positive?", you ask. Think about it. You are responsible for your thoughts, your emotions, your desires, your actions.
When you help others, you do it because it gives you pleasure, or because it gives you less pain than not helping them would give you. By the same token, when you don't help others, you receive the greatest benefit by your actions. This is the way we are built. It isn't good. It isn't bad. It just is. There is no one who has lived, saint or sinner, who has not had the same basic motivation.
The difference between the saint and the sinner is the saint has realized that the personality isn't the sum total of who we are. The saint has realized that helping others brings more pleasure than harming them. The sinner focuses on short-term pleasures that cause long-term pain. The saint focuses on long-term pleasures that can sometimes bring short-term pain. You can be a saint, or you can be a sinner, or, like most of us, you can be a little of both, and each day make choices that will take you to long-term pleasure.