The idea that you can't buy happiness has been exposed as a myth, over and over. Richer countries are happier than poor countries. Richer people within richer countries are happier, too. The evidence is unequivocal: Money makes you happy. You just have to know what to do with it.
So what should you do with it?
Stop buying so much stuff, renowned psychologist Daniel Gilbert told me in an interview a few years ago, and try to spend more money on experiences. "We think that experiences can be fun but leave us with nothing to show for them," he said. "But that turns out to be a good thing." Happiness, for most people not named Sartre, is other people; and experiences are usually shared -- first when they happen and then again and again when we tell our friends.
On the other hand, objects wears out their welcome. If you really love a rug, you might buy it. The first few times you see, you might admire it, and feel happy. But over time, it will probably reveal itself to be just a rug. Try to remember the last time an old piece of furniture made you ecstatic. For me, at least, it's a difficult exercise. The wonder of my potted plants certainly wanes with time. "Psychologists call this habituation, economists call it declining marginal utility, and the rest of us call it marriage," Gilbert wrote in Stumbling on Happiness.