For reasons unexplained, every person in this world is born with a large gaping hole in the center of their chest. And pretty much everyone tries to fill it with something. Some people fill it with religion, others just buy a bunch of stuff and some fill it with other people.
Simply filling this hole with things or people is the definition of happiness. I left mine alone though, because i found out if you run against the wind at the right angle, it makes a whistling noise.