I think we learn to believe that happiness is something we find, get, attain, etc. If we look at dogs, some are just happy, and some aren't. I think people are like this in many ways. Some people are artistic, some mathematical, etc. Although I have no data to back this up, I would suspect that, like many other things, individuals have inherent tendencies to be happier or less happy. I know people who are just, well, bubbly! Like a bird - chirp chirp - happy happy happy - laugh giggle ya ya! And there are other people who just seem to be dour, drab, and generally blah. I would suspect that we start with a genetic predisposition in some way(s), and then as with so many other aspects of our personalities, have that predisposed character worked on by life, the world, etc. I'm sure that, had my chipper friend had her children killed in a prison camp, she might not be such a happy camper.
There's also the difference between "happiness" and "contentment." I think I'm more content that happy. I don't laugh lot, but I'm very contented with life, what I've done, where I am now. I'm happy washing the dishes. I never get up and think, "Uh, I don't want to go to work today! (I'm self-employed with a wife who keeps me insured - so I think that probably has something to do with it!)
