A relatively unknown but controversial work of Mark Twain's is a short Socratic style book entitled What is Man? Twain struggled with himself for 20 years before publishing it because of its controversial nature. In effect he was making the argument that there is no such thing as an altruistic deed, i.e. a helpful action done for someone else with no expectation for recognition or return favor. Instead Twain believed that whatever good deed we perform it is done with selfish intent whether we are consciously aware of it or not. "From cradle to the grave a man never does a single thing which has any FIRST AND FOREMOST object but one - to secure peace of mind and spiritual comfort for HIMSELF."
He gives the following scenario as an example , "A man is waiting at a bus station to reach home in the middle of a storm. A gray-haired ragged old homeless woman approaches him and requests for help. He ponders over for a few seconds and gives her his last dollar. He then walks home in the middle of a storm. On the way home his heart is singing with joy because he did something good. When he reaches home he proudly recounts his tale of charity and earns the respect and affection of his family. He has a hearty dinner and sleeps well that night, knowing how benevolent he has been to the old lady. That is a very good return on an investment of one dollar." Therefore, what Twain concludes is that though it was in fact a good deed the man performed, the real reason the man gave the old lady his fare is because if he didn't he would suffer a guilty conscience and so he did it to spare his peace of mind, not to mention the praise he received from his family. Thus, in fact it was a selfish act.
The idea that there is no such thing as an altruistic act would seem to cast a dark shadow on humanity as we think of any charitable or friendly act we have done can be attributed not solely to our wish to be a good person and help others, but rather to our innate desire to preserve our own peace of mind and sense of worth in the eyes of others. Does this mean we should not try to be selfless and help others in need? Of course not, but it does give us more insight into human motivations--namely, we are all selfish, greedy bastards at heart:) Yet, if we can help others and it happens to help our peace of mind and feeling of worth then it is a win-win situation and we all go home happy!