Is knowledge an obstacle to teaching?

To teach a topic or a skill, it is important to know the topic thoroughly. This idea would seem axiomatic, a virtual truism. The kindly mentor who teaches you chess must be familiar with the game, its goals, and basic moves. It makes inherent sense to assume that knowledge of a topic will enable an individual to teach that topic to others. This principle has been used in industry and virtually all forms of employment for several hundred years. Many areas of employment involve considerable levels of training, and instructors are drawn from the ranks of individuals deemed successful in plying their craft. Such ideas are incorporated in the rich notion of apprenticeship. The apprentice learns the craft through direct interpersonal contact with a master or expert. Within many fields, it is mandatory for experts to share their knowledge with newcomers.