> Ken Thompson has an automobile which he helped design. Unlike most automobiles, it has neither speedometer, nor gas gauge, nor any of the other numerous idiot lights which plague the modern driver. Rather, if the driver makes a mistake, a giant “?” lights up in the center of the dashboard. “The experienced driver,” says Thompson, “will usually know what’s wrong.”

-- The Unix Hater's Handbook pp. 57

"Note the consistent user interface and error reportage."

I usually knew what I had done wrong. (Really). :-)