[nashashmi]

You could also ask the same question to why dumb people are happier. What is it about intelligence that robs people of joy?

[aleph_minus_one]

> What is it about intelligence that robs people of joy?

A hypothesis: intelligence makes it possible to realize how unfair you are treated by other people and society.

This is also a premise in the respective part of the well-known science-fiction novel "Flowers for Algernon" by Daniel Keyes.