Gladwell wants to demonstrate that there are things about many peoples' successes that are not obvious at first. There of course is a need for talent and for hard work and ambition but he points out some of the less obvious factors that might make a difference in someone's development or the opportunities they have.
One of the things that many critics and readers suggest about Gladwell is that he wants to make the things we think of as impossible or only for the people lucky enough to be born with amazing talents a bit more understandable and a bit more possible. He writes about the magic number of 10,000 hours being the key to success in any endeavor and here he adds to that formula the previously unexamined possibilities and steps one might need to take.
For example, hockey players born closer to January 1 are somewhat more likely to be afforded certain opportunities because they have extra time to develop and be chosen for all-star teams and the like over their peers who are born earlier.
He also suggests that genius can be a result of the 10,000 hours of practice as well as the advantages accrued by birth date, being in the right place at the right time, etc., that compound to make this type of success seem more attainable.