"I like seeing the unfriendly paper lady. Every morning I smile and wave and she has NEVER returned it. This sounds weird, but it makes me appreciate the fact that I AM happy enough to wave and smile at others. One day... "
Not sure that this is right on point of the original post, but it seems in the neighborhood. I certainly do my best to have an attitude that spreads more positive than negative during the day. And I think it does make a difference out there in the world. Whether it is an obligation or not, I suppose it is up to you to decide.