|Summing up Mr. Ericssons research in his book "Outliers," Malcolm Gladwell observes that practice isn't "the thing you do once you're good" but "the thing you do that makes you good." He adds that intellectual ability - the trait that an I.Q. score reflects - turns out not to be that important. "Once someone has reached an I.Q. of somewhere around 120," he writes, "having additional I.Q. points doesn't seem to translate into any measureable real-world advantage."
None of this is to deny the power of practice. Nor is it to say that it's impossible for a person with an average I.Q. to, say, earn a Ph.D. in physics.