Yet this triumph has come at a cost. In order to appeal to other economists, behavioral economists are too often concerned with describing how human behavior deviates from the assumptions of standard economic models, rather than with understanding why people behave the way they do.

Consider loss aversion. This is the notion that losses have a bigger psychological impact than gains do — that losing $5, for example, feels worse than gaining $5 feels good. Behavioral economists point to loss aversion as a psychological glitch that explains a lot of puzzling human conduct. But in an article published this year, the psychologist Derek D. Rucker and I contend that the behaviors most commonly attributed to loss aversion are a result of other causes.

For example, in a classic experiment, participants who were given a mug demanded, on average, about $7 to sell it, whereas participants who were not given a mug were willing to pay, on average, about $3 to acquire one. This finding has been interpreted by behavioral economists as evidence for loss aversion: The loss of the mug was anticipated to be more painful than its gain was anticipated to be pleasurable.

But Dr. Rucker and I note that there is an alternative explanation: The participants may not have had a clearly defined idea of what the mug was worth to them. If that was the case, there was a range of prices for the mug ($4 to $6) that left the participants disinclined to either buy or sell it, and therefore mug owners and non-owners maintained the status quo out of inertia. Only a relatively high price ($7 and up) offered a meaningful incentive for an owner to bother parting with the mug; correspondingly, only a relatively low price ($3 or below) offered a meaningful incentive for a non-owner to bother acquiring the mug.

In experiments of our own, we were able to tease apart these two alternatives, and we found that the evidence was more consistent with the “inertia” explanation. Dr. Thaler has dismissed our argument as a “minor point about terminology,” since the deviant behaviors attributed to loss aversion occur regardless of the cause. But a different account for why a behavior occurs is not a minor terminological difference; it is a major explanatory difference. Only if we understand why a behavior occurs can we create generalizable knowledge, the goal of science.