According to surveys, Nigerians are happier with their lives than the people of any other country. The USA came in 16th.
Hey, did we mention that the average Nigerian makes $300 a year? That's less than a hundredth of what the average American makes. America being the country that hands out 120 million prescriptions for anti-depressants every year.
China is turning into a great object lesson in this, as their economy explodes and incomes skyrocket, but levels of happiness and personal satisfaction are dropping at the same rapid rate.
There's a couple of reasons for it. First, your brain adjusts feelings of happiness downward after you've reached some goal or other. It regulates the good feelings, presumably so that you have motivation to reach the next goal instead of just lounging by the pool for the rest of your days.
The second one is that as social creatures, we compare ourselves to our neighbors. This is why executives can cry about the $500,000 salary cap that comes with taking government bailout money. Their friends are making $3 million a year and live in igloo made out of cocaine. We can laugh at their complaints, but of course then you're giving the Nigerian permission to laugh at yours. That guy made 100 times more than you, you make 100 times more than the Nigerian.