One minds the train, one trains the mind.
or
50. One to screw in the light bulb and the remaining 49 to guard him .
or
Two. One to assure the everything possible is being done while the other screws the bulb into the water faucet.
or
1,000,001: One to change the bulb and 1,000,000 to rebuild civilization to the point where they need light bulbs again.
or