You asked..
> how do you explain the very large number of people who spends tons of time and energy trying to get good at maths but fails to even grasp simple concepts like calculus?
One answer, as vector_spaces said, is that the learning environment can completely change the outcome of this effort. You agreed:
> Circumstances matter
It's true that talent being a factor doesn't contradict that, but given how homogenous early-life learning environments are, it's -extremely- difficult to tell whether a person "failed" because of lack of talent, vs. lack of the right environment to experiment and learn.
Basically, because a "wrong environment" fail looks like a "lack of talent" fail, I believe a lot of talented people don't find out that they have the talent in the first place, as they believe that an attempt in the wrong environment is as good as any attempt, and never try again - particularly if they've been chastised and humiliated -during- that learning process, as vector_spaces was.
In any case, the reason I wanted to jump in was because of your original statement:
>I don't think this is because people told them anything
I would just ask that you reconsider that position, based especially on your agreement that "circumstances matter." Thanks for reading.
[edit: linebreaks]