You can always tell the “prisoners” by their demeanor. When they walk into the classroom their demeanor bellows, “I’ve been in this business 20 years. Come on! What are you going to teach me?”
That all-knowing, already-competent attitude is widespread among people who are actually incompetent. A Cornell University study showed that the people who think they know it all, really don’t. An I-already-know-everything attitude is a sure sign of a person’s incompetence.