Most people think that “stupid” and “smart” are intrinsic characteristics, perhaps immutable, “just the way” some people are. This is false. We all know plenty of “stupid” people who are keen in very smart ways, and plenty of “smart” people who make very stupid mistakes.
“Smart” is a skill and discipline of study, and thinking. “Smart” is considering carefully one’s emotions, how they influence and often times control your behavior. “Smart” is pondering every context for any decision, examining a wide swath of potential influences.
“Stupid” is simply the abdication of studying any of those things.
This is good news, because anyone can study. Anyone can be “smart” in virtually any way.