Notice how rarely anyone is argued out of a good excuse, and how often they are simply moved past it by a change in circumstance. 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. It is tempting to call this irrational. It is more useful to ask what it is for. The usual story is that we are careless calculators. The better story is that we are careful about the wrong things.
Where the model breaks
We describe the departure from the model as an error. We might equally describe the model as a hopeful guess about us. Nobody sets out to be governed by a good excuse, yet it shapes an astonishing share of the ordinary day. The remedy is rarely exhortation. It is a change to the situation so that the easier choice is also the better one. A better account of choice would begin with the ordinary case rather than the laboratory one.
