As an introvert, I tend to agree with the author. Introverts generally make up the extreme ends of the population distribution in terms of being "successful", success being defined the way it is generally accepted. On the other hand, extroverts are spread out much more evenly. For example,the CEO of a big corporation might be an introvert, but most of the middle level managers are extroverts. Then there are those introverts who find it difficult to move up in the management hierarchy, for one reason or the other. I believe that those who are exceptions are so in spite of being introverts and not "because" they are introverts.