This question reminds me of a particular science class in high school taught by Mr Ng. The topic was atomic fission and Mr Ng made a statement about fission that was obviously wrong. I can't remember what he said but I knew that he was wrong as I had done some reading outside of class. I think it was then that I learnt that teachers are human and fallible just like the rest of us.
Or, to put it in a wider perspective, those that are in positions authority or power are not necessarily that much better than the rest of us and that they may not always know what is best.