What struck me was that IQ was not the only difference between my best and my worst students. Some of my strongest performers did not have stratospheric IQ scores. Some of my smartest kids weren’t doing so well. And that got me thinking. The kinds of things you need to learn in seventh grade math, sure, they’re hard: ratios, decimals, the area of a parallelogram. But these concepts are not impossible, and I was firmly convinced that every one of my students could learn the material if they worked hard and long enough.

https://www.ted.com/talks/angela_lee_duckworth_grit_the_power_of_passion_and_perseverance