- Happiness is fixed, perhaps. Short-term, it isn't (coke and hookers work!). Long-term, it is. People fall back to a baseline. So then, being smart doesn't help you.
- Dumb people might be misreporting their happiness. So smart people are making themselves happier, but all the studies are done on self-reported happiness, and the dumb people report that they are happier than they really are.
- There's a difference between intelligence and wisdom: if you're intelligent, you have good models. If you're wise, you make good decisions. You might think that you need to be intelligent to be wise, but you also need wisdom to navigate uncertainty, ie you need to exercise your decision making for when you don't have a good model. Dumb people have to do this a lot.
- It may just be that you can make yourself happier, but being intelligent doesn't give you differential access to the levers that you need. Eg to be happy maybe you need an active social life. Well, there's no particular reason having high IQ would help that. We generally have a tendency to think that IQ is a kind of magic substance that can do anything, but why would that be?
- Being smart could actively harm your happiness. I told my kid he needed to wait for his friends to grow up, they will stop only caring about football (luckily the prophesy came true and they are having a great time in their little nerd group). Another friend has the same problem with his kid, they just don't have the social ties available yet. BTW, I really do think there's something to this one, you need the social side to be happy. There's a few HN people who also give me that "finally found my tribe" vibe when they write. I met a guy on the train who saw me coding, and he had the same story.