There can be a situation of getting too far away. Really knowledgeable people sometimes get lost in their reality or get used to situation when small percent of students do understand their material due to better background and others don't that they just slip into delusion that everyone is getting more stupid and there's no need to go with the time forward. And, though, their proficiency in discipline can be over the top, the proven overconfidence in it, and the less so about themselves, get their communication skills and ability to teach more and more dull, and nothing could be done due to authority gained.