Reflections on the correlation between intelligence and success

Having recently reread Malcolm Gladwell's excellent book: Outliers - the story of success, I've been thinking about the correlation between high IQ and success in life. I think I may have come up with a nice way to clarify Malcolm Gladwell's conclusions. Malcolm writes that to succeed in a given field you need to pass a certain threshold of intelligence, but that having more intelligence than the required threshold will not increase your chances of success.