“Assume a can opener”. That’s the punchline to an old joke about economists. The setup is that the plane jetting this year’s Nobel Prize winners off to Stockholm is forced to ditch in the North Sea, leaving the laureates in Chemistry, Physics and Economics stranded on a small uninhabited island. All they can salvage from the wreckage is a very large can of soup.
Each proposes a method to open it based on his own notable expertise. The physicist recommends heating it until the can begins to swell. The chemist agrees and starts looking for phosphorus and sulfur to make a crude match to start a fire. The economist waves them off: “Let’s just assume we have a can opener”.
The assumptions of economists never fail to induce a giggle.