When I was in college, I got a degree in Economics, much to my lasting surprise. Here is the deepest, truest thing I learned about economics in four years of study—not the only thing, but the essential point, not to be forgotten.

Once an engineer, a physicist, and an economist were stranded on a desert island with only a cigarette lighter and a can of tuna fish. The engineer quickly gathered driftwood and built a fire, but the can of tuna fish presented a problem. They sat around the fire and discussed strategies for opening it as they got hungrier and hungrier.

The engineer said, “I know! There are some sharp rocks over there. I’ll go grab one, and bash at the can until it breaks open.”

The physicist said, “No, no, no, you’re working too hard. Just put the can in the fire. The heat will make the contents expand, and eventually the can will burst open.”

The economist just chuckled and shook his head, and said, “You’re both working too hard. First, you assume a can-opener!”

Those who might contest this can go look at Exhibit A, in which a finanical analyst discusses the problem of trusting financial models with shaky foundations.