This is a famous joke about economists and rational-choice theorists in social sciences. I’ve heard this a couple of times in class when I was in a political science department. I found two versions of the same joke:
An economist, a physicist, and a psychic find a can of food while they are stranded on a desert island. The physicist says that they should use their eyeglasses to focus the sun on the can to burn a hole in it. The psychic argues that they should focus their mental energy on the can to pry it open. The economist shakes his head and says, “Why don’t we just assume that we have a can opener?” Quoted from here.
Three people are alone on a desert island: an engineer, a mathematician and an economist. They are starving and don’t have a thing to eat, but somehow they find a case of bean cans washed up to shore.
The engineer says: let’s hit the cans with rocks until it opens.
The mathematician has another idea: “No. I’ll calculate the speed and trajectory to throw it against the rocks and burst.”
Finally, the economist says: “Assume we have a can opener….”Quoted from here.
It captures the fundamental critique towards economists (and rational choice theorists). “Let’s assume people have perfect knowledge about the product…” “Let’s assume all people act based on their cost-benefit calculations….”