Adapted from a joke about economists:

A quant(financial engineer), a mechanical engineer, and a chemical engineer are shipwrecked on a deserted island. They are starving, and are tired of eating coconuts. They come upon a can of food on the beach....

The mechanical engineer says, 'let's wdge the can between these 2 palm trees and rig a branch to chop the top of the can off' The other two quickly point out that this will destroy the can and likely send the contents all over the place, wasting them...

The chemical engineer says, 'let's take the sea water and reverse the polarity of the water extracting the salt to make an acid and then burn one end of the can off' The other two quickly point out that while this is clever it will likely ruin the contents of the can.

The quant says, 'let's make a simplifying modeling assumption.... let's begin by assuming that we have a can opener'

:-)