People do all kinds of their things, naturally, trying to make themselves happy. Let us see if we can summarize stuff people do in a set of few generalizations:

1. Learn some skills, trying to be the best in whatever they do, and accumulate attention and admiration as much as possible on the way. People do these stuff, naturally, to attract the best possible mate, and naturally, breed.
2. For those who are succeeded in gaining some extraordinary skills, but the skills they happened to choose, unfortunately, doesn't help them in getting the relatively best mate possible (video game champion, for instance), then they will simply try to go all the way as far as their own Symphony No.9. Poor Beethoven.
3. For those unlucky enough to gain any useful skill, they will simply, if possible, breed as much as possible.
4. For the unluckiest of all, no skill and no chance to breed, they just go home, and if possible, watch TV, eat junk food and get fat. Or the no less unattractive opposite.

That's pretty much what most people do, despite some statistically insignificant exceptions. The question is, what is it that people think can make them happy? Why do people imagine that breeding and being famous can make them happy?

What does breeding and getting rich or famous have in common? It is to have more people that potentially would respect and appreciate whatever crap we do. It is to imagine that there would be more people who would miss us when we're gone. To put it simply, most people have this simple equation of happiness:

Level of our happiness = c * (number of people crying when we die)

Where c is a changing constant that changes so much it is not a constant at all. So here we are all, collecting people to cry on our grave.