The thesis of Dan Ariely's new book, Predictably Irrational, is that "people often make decisions that seem to defy logic--but they do so in very predictable, consistent ways." It sounds like a good book, and I'm looking forward to reading it. But one of his experiments, described in this MIT Tech Talk article, doesn't really make sense.

Ariely and his students went around and left six-packs of Coke in randomly selected dorm refrigerators all over campus. When he checked back in a few days, all of the Cokes were gone. But when he later placed plates of six loose dollar bills in those same refrigerators, not a single bill was missing when he checked back. Even though the value was comparable--and thus the situations were supposed to be equivalent--people responded in opposite ways.
The problem is with the idea that "the value was comparable -- and thus the situations were supposed to be equivalent." The value is comparable in the sense that the price of a can of soda is around a dollar. But to a person standing thirstily in front of a refrigerator, the value of a can of soda is greater than a dollar. Try leaving a six-pack of Coke and six dollar bills on a municipal garbage can and see which one disappears first.

Update: Good lord! Ariely himself (the Alfred P. Sloan Professor of Behavioral Economics at MIT's Sloan School of Management) responds, both courteously and informatively, in the comments. The internet is amazing.