If you take a bale of hay and tie it to the tail of a mule and then strike a match and set the bale of hay on fire, and if you then compare the energy expended shortly thereafter by the mule with the energy expended by yourself in the striking of the match, you will understand the concept of amplification.

In The Chip War : The Battle for the World of Tomorrow (1989) by Fred Warshofsky, p. 21.