Naturally..

As I read about Thomas Hobbes' Leviathan in Wikiquote. One sentence stuck out in my mind.

"Hobbes finds three basic causes of the conflict in this state of nature: competition, diffidence and glory. The first maketh men invade for gain; the second, for safety; and the third, for reputation. "

In my Philosophy 150 class, we're discussing human nature and psychological egoism.
Psychological egoism is basically stating every thought and action we do is purely for selfish reasons. Keep in mind, "selfish" is not a bad thing always. 
Hobbes' 3 causes of conflict would seem to fit perfectly into what psychological egoism is.

Competition: This is easy. Of course everybody enjoys winning. The term "take one for the team" could be argued that one is selflessly helping out their teammates but more often than not, that one will be praised for their aid.

Diffidence: A lack of self confidence. How can anybody call this selfish? When someone is too shy to do something or take an initiative, isn't that selfish? He won't take action because HE doesn't feel confident or comfortable.

Glory: My junior year in AP Literature, we talked extensively about reputation and what can happen if you gain a good or bad rep. All in all, I think everyone can agree glory is ultimately for selfish reasons.

Human nature is a curious thing. Whether or not you agree with psychological egoism, it is interesting to think of the intentions we have when making a decision.

Food for thought.