Some are fooled into not recognizing their own selfishness being satisfied by some of the rewards and call it altruism. While others seeking those same rewards find a good deal of self satisfaction in their own selfish giving.
This concept can be expanded all the way to the risking of ones own life for others. But taking it one step beyond that to the actual giving of ones life for another brings rationality in to question in most, but not all cases. For example, a mother giving her life to save her child's life, I think could be called an act of rational selfishness, in most cases.
This view of altruism and selfishness I learned from arguing with the writings of Rand. Its been so many years since I read Rand's stuff, that it is now impossible for me to draw a line between what is from Rand and what is from myself and others. But I must giveher the credit for the insight, even if all of it is not hers.
But this explains nothing. Why self-sacrifice delivers any reward? Is a man who is selfish in the traditional sense, -- e.g. greedy, -- ethicaly equal to a man who gives his excess away, and receives the moral gratification?