One day I was in a very-low priced PC store looking for a suitable machine. Another man was also there in the store talking with the store owner as follows: Man: I want to have the system an extra meg. of memory. Owner: No problem. That will cost you only $75. Man: But, how and when can I use the extra meg? Owner: You can use it whenever your programs need it. Man: Then what is its use if I can't use it all the time? Owner: (After a pause) You know, it is just like the extra wheel in your car.
(From the "Rest" of RHF)