Can anyone be taught anything?

Assume a person without a congenital disorder like Down’s Syndrome and assume a sufficient motivation for learning. Can any such a person could learn to fly an airplane, play the violin, understand the theory of relativity or run for political office?

I realize that people have natural aptitudes in different areas, so some people will learn more quickly than others. Is it just a matter of time then, or are there blind spots and deficiencies that we have that make learning certain things impossible? The mathematician John von Neumann said, “In mathematics you don’t understand things. You just get used to them.” To what extent is that true of not just mathematics, but of everything else? Is it just a matter of acclimating oneself to certain concepts, which would imply that learning these things would be open to anyone?