The most valuable thing for the serious student is negative feedback – to be told when they're getting it wrong. And in any open system above a certain size negative feedback abounds – it is the fundamental law of the universe – karma. Things and situations tend to regulate themselves if allowed to. The problem is when the system closes, either in on itself because it is too small or insignificant, or because there is a positive force overwhelming natural response – where the negative is effectively banished because it is deemed to be bad. This happens often in taiji schools, where unquestioned principles tends to reign, and where the students, instead of being encouraged to test the prevailing dogma, are expected to take it all on faith, and any doubt or any unorthodox input is interpreted as the evil ego rearing its ugly head. Such a school, in my opinion, is already corrupt.