The physicist, engineer and mathematician

Physicists see equations as a reflection of reality.
Engineers see reality as a reflection of equations.
Mathematicians haven't made the connection.

One night a physicist, an engineer, and a mathematician each awoke to a fire in their kitchen. The physicist calculated the precise amount of water necessary to extinguish the fire, measure out just that amount of water, poured it on the fire, and went back to bed. The engineer poured water on the fire till is went out, added some more for good measure, then went back to bed. The mathematician proved that is was possible to extinguish fire with water, then went back to bed.