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…
Happiness is just chemicals, it has nothing to do with that.
Your choices, (in)actions, and perceptions are things that can cause the release of said chemicals.
Your intelligence, as well as abilities and habits, can effect how (or even whether you can) do or do not do things.