The measure that matters is not what people say about expertise but what they do when nobody is scoring. Ask most people why they did what they did and they will give you a reason; ask them again a week later and the reason will have quietly changed. The usual story is that we are careless calculators. The better story is that we are careful about the wrong things. What looks like expertise from the outside is usually something simpler from the inside: tiredness, a deadline, a wish not to look foolish.
The cost of being right
A better account of expertise would begin with the ordinary case rather than the laboratory one. The textbook treats expertise as a preference to be revealed. In practice it is a story we tell ourselves after the fact. There is a version of this essay that ends with a policy prescription. This is not that version; the mechanism is interesting enough on its own. Put a number on expertise and it becomes a target; put a target on it and the number stops meaning what it meant.
