Comment by jodrellblank

In the context of the parent comment "I've never understood how someone could master a subject and yet be unable to answer any questions about it.", isn't this your literalist side jumping in joy at being able to say "Aha, aha, I can think of a group of people who have mastered a subject but cannot answer questions about it"?

Except, they can answer questions to show what they know, they just can't answer your carefully selected subset of questions with the exact answers you demand using the terminology you demand.

Draw an arbitrary line around the allowable questions and you can make every group of experts, "people who can't answer questions about it". But what use is that?