The vast majority of your conscious hours, through your childhood, teens into adulthood, are spent in a process of systematic rape of your mind, of your spirit, of your joy for learning, of your ability to scan, of your integrity, of your personal power, The destruction of all of these things, is called school. School's a bad thing. Not in principal, but in the way it's currently done, it destroys children and the adults they will be.
Without the artificial structures of school, they would be social creatures, creatures of the pack, but they would base their social standing on how fast you can run, who can climb the highest in a tree, who can find the most cool things, who can tell the jokes that make everybody laugh. Organic, natural things. At school, you learn to evaluate your social status instead by your ability to do well in school. You call this "smart", but it has nothing to do with intelligence.
The only thing that intelligence tests measure, is how good you are at taking intelligence tests. Nobody knows what "smart" and "intelligent" really means. "Intelligence" doesn't really exist. Some people are better at math, some people are better at spatial manipulation, some people are good at social things and others are better at baking things. Yes, there are people who are better at things than others. Yes, there are people who are good at learning, so they look like they are intelligent, but it's just one thing they're good at. It's the familiar idea of measuring the intelligence of a fish by it's ability to climb a tree.
A number of people in this process handicap themselves by insisting that they are "smart". And it's usually the ones who aren't: the ones who failed at school, or who got through school by endless repetition but never actually understood anything. They're not mentally adroit people, but they keep claiming they are so smart. You find it more amongst right-handed people, "smart" is a thing they really want and they can't find it, so they start just claiming they are and beating up anyone who disagrees and refusing to learn anything new that makes them feel stupid, so in fact they make themselves more stupid.
For those of you who have ever called anything stupid, you probably have some of this. If you call someone stupid as a derogative term, then you feel that this is an important thing. Smart doesn't exist. You're not smart. Stop fighting to protect your idea that you're smart, and the things you do to prove to yourself and others that you're smart. Check if you even like any of those things.