The UNIX Philosophy
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 he, "will usually know what's wrong."
Original source unknown; found on Joseph Evans' (Electrical and Computer Engineering professor at Kansas University) door.