Oftentimes, when you design programs or objects or anything else, you have to make sure that people who lack certain prerequisites can still use what you designed. They must not fail badly, and they must still be at least a bit usable in extreme circumstances. For example, a car’s doors must always open from the inside, even if the battery is dead and the locks are magnetic. Therefore, the mechanism opening the doors must be purely mechanical.
The best example of a design that degrades gracefully is the escalator. The escalator is a marvel of modern engineering. It takes you up or down, much like an elevator, but the vast difference is what happens when the power is cut. While an elevator will trap you inside and require you to call the emergency personnel to get you out after a lot of anguish and trouble, escalators simply (get this) become stairs.
I’m telling you, if every designer had the escalator in mind, the world would be a better place. When cars ran out of gas, you could use the pedals they would have to make them run, as you do with bicycles. That’d be great! The other three people in the car never do anything anyway, they only mooch off my gas! You could make them work and it would be good exercise.
Apparently, a Jesse W. Reno invented the escalator (or so Wikipedia claims). Unfortunately, his name has been lost in time, since noone knows who he is. Regardless, my hat is off to you, sir.