I drove to the store last night only to find on arrival that I had forgotten my wallet. I returned home frustrated and ready to veg out in front of the tv. It occured to me, however, that my earlier trip was a sunk cost. If the trip was worthwhile the first time it must be worthwhile to return (not so much time had passed as to change the utility of the calculation). I still felt frustrated and I didn’t really want to return but I forced myself to behave like a rational utility maximizer. As I headed back, however, I felt better. Reason and emotion cohered once again as the sunk cost became psychologically sunk.
Score one for economics. A sunk cost is only sunk if you choose to ignore it and economics helps us to do this. But note to self: have more sympathy for students who find the economic way of thinking to be unnatural. Often, they are right.