The correct, original Murphy's
Law reads: "If there are two or more ways to do something, and one
of those ways can result in a catastrophe, then someone will do
it." This is a principle of defensive design, cited here because
it is usually given in mutant forms less descriptive of the
challenges of design for lusers. For example, you don't make a
two-pin plug symmetrical and then label it `THIS WAY UP'; if it
matters which way it is plugged in, then you make the design
asymmetrical (see also the anecdote under magic smoke).
Edward A. Murphy, Jr. was one of the engineers on the rocket-sled
experiments that were done by the U.S. Air Force in 1949 to test
human acceleration tolerances (USAF project MX981). One experiment
involved a set of 16 accelerometers mounted to different parts of
the subject's body. There were two ways each sensor could be glued
to its mount, and somebody methodically installed all 16 the wrong
way around. Murphy then made the original form of his
pronouncement, which the test subject (Major John Paul Stapp)
quoted at a news conference a few days later.
Within months `Murphy's Law' had spread to various technical
cultures connected to aerospace engineering. Before too many years
had gone by variants had passed into the popular imagination,
changing as they went. Most of these are variants on "Anything
that can go wrong, will"; this is correctly referred to as
Finagle's Law. The memetic drift apparent in these mutants
clearly demonstrates Murphy's Law acting on itself!
