Why does Gladwell insist that IQ is not the determining factor in one's ability to achieve success?

Gladwell argues that success is shaped by a variety of factors beyond IQ, such as social skills, perseverance, and opportunity. He believes that success is a result of a combination of both innate ability and external factors, rather than just raw intelligence. Gladwell also emphasizes the importance of hard work and seizing the right opportunities in achieving success, rather than solely relying on IQ.