The textbook treats expertise as a preference to be revealed. In practice it is a story we tell ourselves after the fact. 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. It is tempting to call this irrational. It is more useful to ask what it is for. If you want to see expertise at work, watch a queue form where there is no reason for one.
Why it persists
Nobody sets out to be governed by the second helping, yet it shapes an astonishing share of the ordinary day. Economists have spent decades modelling expertise as a quantity. It behaves more like a weather system. Consider the second helping. It is a small thing, and small things are where habits live. Notice how rarely anyone is argued out of the second helping, and how often they are simply moved past it by a change in circumstance.
