It is controversial (though a widespread belief among philosophers), but I believe that human talent is entirely a function of the interaction of genes and environment. We don't control the neighborhood in which we are born, the school in which we're enrolled, the values instilled in us, or our temperamental inclination to learning. I believe, for similar reasons, that we don't control our own effort. Humans don't stand apart from the naturalistic universe, but are a part of it. Others claim that while genes and environment play the largest role in determining our talents, we also have a degree of volition in those constraints with which to make better or worse use of those conditions, and for which we should be awarded responsibly. Either way, on the strong or weak version, our talents are largely our of our control, and it is therefore unfair to heavily reward or punish people for them.

I'm also extremely sceptical of the idea that high-earning jobs demand more effort. I have a PhD and it required a fair amount of work. My immediate family were all in unskilled, low-paying jobs which they found boring, and derived little satisfaction from. Who put more effort in? We both had to work, but I found it interesting and fulfilling, whereas they did not. For them, there was a far greater gap between what they were doing and what they wanted to be doing. I think it's obvious that their jobs required more effort in any morally relevant sense. The relationship between effort and pay seems fairly incidental, but a general trend is that the more you are paid, the more likely the job is to exercise and develop your faculties. In this respect, the trendline goes from harder to easier with pay.