Do not instruct someone who never listens to you (P. Onch. 7/5).This seems self-evident. If someone is not going to listen to you, it is a waste of time talking to them.
Years ago, a colleague called me up and asked me my opinion about a certain point of ancient Egyptian. He was not a specialist in ancient Egypt and I appreciated him asking me about it. It became clear in the course of the conversation, however, that he had already made up his mind about how the point ought to be, and did not appreciate me saying that ancient Egyptian did not work the way he thought it did. For all the effect it had, I might as well have been talking to a brick wall. He persisted and published his opinion regardless of the fact that it had absolutely no support for it. How sad!