An engineer, a social worker and an economist get stuck on a desert island. They find crates and crates of food but no can-opener.
The engineer gets to work designing and building an ingenious contraption to open the cans using a complex assembly rocks and rope and pulleys. It takes two days to build and there's constant tinkering involved to keep it working but each can opens as cleanly as with a store-bought can opener
The social worker smashes each can with a small rock. About half the contents gets splattered on the sand, but the social workers says "hey, we've got plenty, the important thing is we get some food out quickly"
The economist sits down and says "ok, let's just assume that there WAS a can opener..."