There are other reasons why many smart people are unhappy and it has nothing to do with how successful one is:

Solomon said:

16I said to myself, “Behold, I have grown and increased in wisdom beyond all those before me who were over Jerusalem, and my mind has observed a wealth of wisdom and knowledge.” 17So I set my mind to know wisdom and madness and folly; I learned that this, too, is a pursuit of the wind. 18For with much wisdom comes much sorrow, and as knowledge grows, grief increases.…