I read a quote recently (and I can't for the life of me remember who said it!) that went something like this:
"The reason for unhappiness is that 99% of the things you do in life, you do for your self. And there is none."
I'll admit it took me a minute to understand what this quote was trying to say, but I think there's something to it. We humans have the need to feel as if we're a part of something larger than our perceivable selves. Maybe its because we're pack animals living increasingly more isolated lives. Maybe its because of, as Marx called it, "alienation" from meaningful work and production. For the Buddhist, unhappiness is because of suffering that is linked to desire. To reduce suffering, one must simply reduce desire, which is, of course, easier said than done!
In truly selfless acts, however, we go beyond the self and are instantly a part of something larger. The feeling of communion with something larger, even it is just a piece of the proverbial pie, and not the Whole itself, is clearly there in social justice movements, religious congregations, and acts of montetaru generosity.
Hmmm, perhaps Durkheim was right after all.