Three guys are alone on a desert island: an engineer, a biologist and an economist.
They are starving and don't have a thing to eat, but somehow they find a can of beans on the shore.
The engineer says: "Let's hit the can with a rock until it opens."
The biologist has another idea: "No. We should wait for a while. Erosion will do the job."
Finally, the economist says: "Let's assume that we have a can opener".