I remember seeing an episode of Friends many years ago where Phoebe and Joey argue whether or not a truly selfless deed exists. According to psychologists, it may not.
Not because of intent, but because of reality. You may do a great deed because it should be done, but you’ll benefit from it as well.
For example, one study showed that, neurologically, giving money to charity activates the same reward centers of the brain as sex, money, food, and drugs. Another study reported that people who committed random acts of kindness felt happier for weeks after the event.
So as you go into this Holiday season, why not give back and give yourself some euphoria at the same time. Volunteer at a food shelter, participate in a food-drive, give a coworker my book… Not only will the other person benefit, you’ll also be happier. Neural responses to giving. Harbaugh, William T. and Ulrich Mayr. “Neural responses to taxation and voluntary giving reveal motives for charitable donations,” Science, 316, 2007.
 Pursuing sustained happiness. Lyubomirsky, Sonja and Chris. “Pursuing sustained happiness through random acts of kindness and counting one’s blessings,” Department of Psychology, University of California, 2004.