According to a very good story about the advent of Murphy's Law, an expensive rocket sled experiment was ruined when a connector was put together wrong. What became Murphy's Law started out as "If there are two or more ways to do something and one of those results in a catastrophe, then someone will do it that way."

The meaning from an engineering perspective is simple - design things so they can only be connected correctly. Look at the back of a computer at the connectors. Virtually all of them are designed so that it isn't possible to connect things incorrectly.

Unfortunately, it seems some engineers just aren't getting the word. The 5th prototype of the V-22 Osprey crashed on its first flight because a connector was connected backwards, sending incorrect control inputs to the system. An Airbus airliner almost crashed several years ago when the same thing happened - a connector on the pilot's flight controls was connected backwards, reversing the control responses. Fortunately, the other pilot was able to take control. Likewise, that gravity sensor on Stardust was designed so that it could be installed either way and was installed backwards, causing huge problems and loss of a lot of data.