@DrFunk,
Sometimes I give people a CD that I like, hoping it will enrich their life in some way. I don't expect them to give me anything back. Maybe a thank you
Something about being social creatures makes it feel good to help people and to give people gifts.
If I am feeling happy, then it becomes my goal to spread happiness around, not to hoard it.
So happy people do good things for people, for free. Angry people, people who feel betrayed by society, usually commit crimes. This very often includes rebellious teenagers full of angst and also impoverished individuals in desperate situations.
You can see how a person's inner emotions can translate into their outward actions.
I think it is human nature to express ones inner emotions outwardly in a variety of different ways.
The best examples of this can be found in art.
Look at different sub categories within a broader genre, like hip hop. You have your "positive" raps like De La Soul and Tribe Called Quest, and you have your "negative" raps like Wu Tang Clan and NWA.
Negative and positive, in this case, don't refer to the value of the art, but the disposition of the sentiments being expressed. The same could be said for human action.