Earlier quoted context omitted.
As I heard someone say, happiness is your reality minus your expectations. Smart people see more variables that could be changed, more components that could be modified, and are less likely to accept things as they are. This creates a false sense of ease by which reality could be modified, and thus higher expectations for the world around them. I suspect this misplaces happiness and contentment, but the two are also…
I think smart people are told much more often as kids how bright of a future they have. So they build up expectations of "succeeding" in some sense (becoming a doctor, getting rich, etc.). These are the sort of expectations you mention in your quote. Not only is there often pressure put on you if you're smart, you adopt those expectations yourself. Or at least hold yourself to that standard. Of course, being smart do…
The only change is that the baseline for unhappiness is higher (so not just food on the table and roof over your head, but a decent career and mid-class lifestyle is sufficient).