Murphy's Law

Murphy's law is a popular adage(an edge is a short) in Western culture that most likely originated at Edwards Air Force Base in 1948.
"The Law broadly states that things will go wrong in any given situation, if you give them a chance"
"If there's more than one way to do a job, and one of those ways will result in disaster, then somebody will do it that way."
It is most often cited as "Whatever can go wrong, will go wrong"
or alternately
"Whatever can go wrong will go wrong, and at the worst possible time,"
or
"Anything that can go wrong, will,"
or even
"If anything can go wrong, it will, and usually at the most inopportune moment"

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.
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.