The criminal misuse of time was pointing out the mistakes. Catching them―noticing them―that was essential. If you did not in your own mind distinguish between useful and erroneous information, then you were not learning at all, you were merely replacing ignorance with false belief, which was no improvement. The part of the man's statement that was true, however, was about the uselessness of speaking up. If I know that the teacher is wrong, and say nothing, then I remain the only one who knows, and that gives me an advantage over those who believe the teacher.