Subject matter experts (SMEs) have something called “unconscious competence.” They are so good at what they do that they don’t know how or why they do it. Many of the smartest things they do are done without a thought.
But why would we ask someone who can’t describe how they perform a task to train someone else? We shouldn’t. Also, because of their extreme expertise, it’s hard for them to put themselves in the shoes of the new learner. So they don’t know