I am reminded of a story about Abraham Lincoln. According to the story, Lincoln was riding with a friend in a carriage on a rainy evening. As they rode, Lincoln told the friend that he believed in what economists would call the utility-maximizing theory of behavior, that people always act so as to maximize their own happiness, and for no other reason. Just then, the carriage crossed a bridge, and Lincoln saw a pig stuck in the muddy riverbank. Telling the carriage driver to stop, Lincoln struggled through the rain and mud, picked up the pig, and carried it to safety.
When the muddy Lincoln returned to the carriage, his friend naturally pointed out that he had just disproved his own hypothesis by putting himself to great trouble and discomfort to save a pig. "Not at all," said Lincoln. "What I did is perfectly consistent with my theory. If I hadn't saved that pig, I would have felt terrible."
(HT Greg Mankiw)