I do not have enough mental strength. Maybe after years and years of dedicating my life to it I might be able to do it at some level. Whatever the case, we can safely say that many people are just more talented than me on a physiological level at chess. It would be absurd to suggest that we are all physically equal.
Again, the question is not if we are all equal or not, but rather, how important is it? Does it form a physical barrier if we are not a certain IQ by say, age 6?
Elubas, I think you hit the key point: "a lot of things go into the making of a great chess player." It just seems to me that some things come easier for some people than for others. I remember my school days when I would have friends that could understand and excel in subjects that took me a lot more effort and I still was not able to reach their levels of expertise.
Again, hopefully I'm not being argumentative, just trying to add food for thought.