"Engineers simply refuse to eliminate a thing they call “safety factor.” They will deliberately over-design and over-build by a factor ranging from two to ten, depending upon the magnitude and seriousness of the consequences if something goes wrong. This does not mean that they have no confidence in their work. It is their statement of reality because they know good and well that sooner or later (a) somebody is going to goof, forget instructions, panic, or try to stretch the design, and/or (b) something in the system is going to malfunction."