I read about a quiet little girl at school that turned out to know all the other kids (eg preferences) better than any other kid. The intro/extro dichotomy has been taken far in mainstream writing, and I think the author is addressing people that have gone too far in the introvert direction, or rather made it a permanent part of their personality.

Also, for those of you who are afraid of being judged when speaking, start by convincing yourself that other people have something interesting to teach you, then ask questions.