What you learn at school are facts, known facts. Your job at school is to accumulate and remember facts. The more you can remember, the better you do. Thos who fail at school are not interested in facts; or maybe the facts are not put to them in a way they find interesting.
Some people simply don’t have a great faculty for memory. It doesn’t mean they are stupid. It means their imagination hasn’t been fired up by academic tuition. People who are conventionally clever get jobs on their qualifications, not their desire to succeed.
Very simply, they get overtaken by those who continually strive to be better than they are. As long as the goal is there, there is no limit to anyone’s achievement.