Right. Grades in itself are often also not a good metric. There are plenty of intelligent kids who just skate through school achieving acceptable yet not amazing results, and you have others who have to work really hard to achieve similar results.

I had a B average at school, no need to study except the day before.

This has caused some issues later in life...

My zero effort, A- average in HS pretty quickly became academic probation in college. It's unfortunately very common, and I was even warned about it before (and while) it was happening.

One thing I learned in college is that grades should be but are almost never an objective measure of how well someone understood the material covered.