I think there is some value in being able to live in the moment, like say a cat: one moment you have a death scare, the next you're kind of hungry or sleepy. I feel that smart people see a lot more in the past, present and future, all the things themselves, and the things behind the things, and it's a whole lot harder to live in the moment and not ruminate and dwell on things.

Alternatively, maybe it's just that overthinking that is driving some aspect of what we call intelligence; the ability to plan and see things in complex layers.

Good amounts of happiness surely require some selective blindness.