The author quotes a wonderful piece of research which found that people are half as good at remembering a face in a photograph, if they've tried to describe it when they first see it. If we only trust our innate and wordless ability to remember a face, we are twice as likely to remember it: a metaphor for general practice. Doctors are being constrained not to rely on their hard-won experience, knowledge and skill, their unarticulated sense of what needs to be done. But instead always to use their conscious brain function to work out a solution. Thus quite possibly reducing their effectiveness by half.
This give a more accurate portrayal of the value of the "unconscious competence" pane of Johari's Window (the other windows being unconscious incompetence, conscious incompetence, and conscious competence). When a person knows their work so well, they don't need to articulate how they know it. This blurb suggests that in some cases, asking someone to explain their thinking actually reduces the value of their unconscious knowledge by forcing them to consider how it is they know something.