Nice example on how machine efficiency doesn’t necessarily equal user efficiency:
For example, which of the following takes less time? Heating water in a microwave for one minute and ten seconds or heating it for one minute and eleven seconds?
From the standpoint of the microwave, one minute and ten seconds is the obviously correct answer. From the standpoint of the user of the microwave, one minute and eleven seconds is faster. Why? Because in the first case, the user must press the one key twice, then visually locate the zero key, move the finger into place over it, and press it once. In the second case, the user just presses the same key–the one key–three times. It typically takes more than one second to acquire the zero key. Hence, the water is heated faster when it is “cooked” longer.
Quoted from http://www.asktog.com/basics/firstPrinciples.html