If you're earning "enough" and you've got a little bit left over, and you're only ever going to have a little bit left over, why not share some of what you've got? But now I've got more than a little bit left over, and I'm starting to think of my money as stackable units.
The New York Times Magazine published a feature about a group of teenagers from very different high schools who have worked together for eight years in a sort of cultural exchange over the class divide. The article focuses on an exercise the kids undergo where they tell each other a story about themselves and then the other person presents it to the group in the first person. Radical empathy!