There are really two versions of selfishness. One is the kind most people think of when you say the word: someone who puts their own needs ahead of the needs of others. The other, more severe version, is the type of person who doesn’t really understand that other people are real. This doesn’t mean that they consciously decide other people are figments of their imagination, it’s more normally subconscious, but where the first type of person considers other people’s wants or needs and chooses their own, the second type never has the fact that other people HAVE wants or needs register on them.
The unfortunate part for both of these people is that human beings are meant to have interactions and relationships with others. Selfish people are very, very seldom happy. The second type of selfish person is even less likely than the first type to be happy. The reason for this is that physical things can only bring temporary satisfaction. As you become accustomed to having them, they fade into the background, and no longer bring much pleasure.
People are different. People are always changing, whether they want to or not. You simply can’t have the same person in your life (or, indeed, BE the same person) next year as this. This makes it much more difficult for people to fade into the background as objects do. It is very difficult to become accustomed to something which is never the same.
Since selfish people, especially the second type, dismiss people, they are left more with objects, which do not change over time, and therefore become boring and fade out of notice. One of the only ways to “reset” this fading out is to take away substantial amounts of the objects someone has. The most common form of doing this is to lose substantial amounts of money, especially if you go bankrupt.
Many times, besides making the person appreciate the objects if and when they re-acquire them, this also has the effect of making them less selfish, as they can now identify more with other people. Which in turn makes them happier. I don’t know, really, any easy way to help someone become less selfish. The only thing that really seems to work is either loss, or very real belief that loss may happen.
If you do happen to know something that works, please leave your answer in the comments.