Which of Gladwell’s arguments fail to add up? (Logically, etc.) Why?

Although Gladwell often emphasizes the role of practice and initiative, he does not deny the role of luck in determining success. After all, a hockey player born in the right month will be granted built-in advantages of increased practice and attention; something similar could be said of a corporate lawyer, industrial tycoon, or software engineer born in the right year. Success, according to Gladwell, is in part the product of numerous arbitrary factors (ethnicity and social class among them) that make remarkable opportunities possible.