Much of what Mr. Gladwell has to say about superstars is little more than common sense: that talent alone is not enough to ensure success, that opportunity, hard work, timing and luck play important roles as well. The problem is that he then tries to extrapolate these observations into broader hypotheses about success. These hypotheses not only rely heavily on suggestion and innuendo, but they also pivot deceptively around various anecdotes and studies that are selective in the extreme: the reader has no idea how representative such examples are, or how reliable — or dated — any particular study might be.
Gladwell highlights the claim of psychologist Anders Ericsson, that effort dominates ability (the 10,000 hours of practice thesis). My opinion on this can be found here, deep in the comments. The evidence is pretty strong in the case of science that native cognitive ability is a prerequisite for success. Practice (effort) is necessary also, but neither alone are sufficient.
...that quote sounds like it could be from Anders Ericsson's research on expertise. I disagree with his conclusions. His studies only show that effortful practice (about 10 years worth) is typically required to reach the highest level of capability. But he then confuses the logic and asserts that practice alone is *sufficient*, when in fact it is only necessary. You need raw ability *and* lengthy practice to reach expertise.
Of course it is appealing for most people to think that Ericsson's model is correct and that effort is all that is required to produce capability, but this claim is very controversial in the psychology community, and I think implausible to anyone who has been around gifted kids/adults.
The Roe study, combined with other studies showing the age stability of IQ (certainly once adulthood is reached), also serves to refute Ericsson. There's clearly some measurable quality, usually present already at an early age, that is advantageous for intellectual achievement. Most people don't have it.
Anders is refuted quite well in papers by leading psychologists like Sternberg (Yale) and in Eysenck's book Genius.
By the way, also contra Ericsson, there are many credible examples of supreme raw talent that didn't require development through 10 years of practice (e.g., Mozart).