My best teachers were also content experts. My worst teachers by a long shot were also content experts, holding, in one case, the research chair of an academic

My best teachers were also content experts. My worst teachers by a long shot were also content experts, holding, in one case, the research chair of an academic department in a renowned research university. Couldn't teach to save his life and was lucky that the tutors put in a lot of extra hours so that around 50% of the enrolled students passed his fairly easy course (it was a revelation that after I had failed, and had to re-sit during the summer, I asked an academic in a related field to coach me based on a text, and his explanations were lucid, to the point, had an expository style that engaged and that he actually wanted to address the material at hand). An intelligent person with some domain knowledge, good teaching materials and firm grasp on how students learn beats someone with all the domain knowledge in the world who is a hopeless teacher, in my experience.