I think there are a couple of things going on that lead to the situation you describe: One, there is a very strong ethos in our culture that the only thing tha

I think there are a couple of things going on that lead to the situation you describe: One, there is a very strong ethos in our culture that the only thing that matters for results is effort. We want to believe that we are in control of our own destiny, and that everyone can each any level of success if they choose to exert the required effort. Any lack of success is tied to a lack of effort (or, occasionally, people will say the lack of success is caused by misapplied effort)... in both cases, the implication is that any person just needs to make the right series of choices to achieve any level of success that is possible. The second thing is that even if we realize that some people won't be able to achieve at a certain level, it is probably still a good idea to act as if they can. Someone who thinks they can achieve something but can't will end up in the same place regardless of that belief, but someone who actually can achieve something will have a different outcome if they believe they can instead of can't.