->''"In 1949, Edward Murphy conducted a rocket sled experiment - to see how much pressure a human being could withstand. Murphy's experiment failed. Spectacularly. Over and over. Needless to say, he didn't start off on the right foot. That's why it's called 'Murphy's Law', because if anything can go wrong; it will! [...] It's on us to take everything that can go wrong, and make it go right. It's on us to try, anyway."''
-->-- '''Meredith Grey''', ''Series/GreysAnatomy'' "It Only Gets Much Worse"

Murphy's Law is summed up as "If something ''can'' be used or done a right way and a wrong way, [[WhatCouldPossiblyGoWrong and the wrong way will lead to catastrophe]], it ''will'' [[LethallyStupid be used or done the wrong way]]."

As originally applied, Murphy's Law -- coined by, and named after, U.S. Air Force engineer [[http://en.wikipedia.org/wiki/Edward_A._Murphy,_Jr Edward A. Murphy, Jr.]]-- was intended not as ironic humor but as a serious admonition to engineers: a device shouldn't be made so that it ''can'' be used incorrectly in the first place, a practice commonly referred to as [[WhoWouldBeStupidEnough Idiot-Proofing]] or "defensive design". Study, for instance, the loss of several F-111 (TFX ) aircraft during the Vietnam War due to the backwards insertion of a graphite pin in the rudder assembly. Had Murphy's Law been heeded, the pin would have been designed so that it ''could not be inserted backwards''. One of Murphy's co-workers would later sum up the engineer's idea as [[DidntThinkThisThrough "If there is any way to do it wrong, [the technician] will [achieve it]".]]

Murphy's Law is also the most commonly used term for the infamously pessimistic maxim, "Anything that can go wrong, will go wrong." The creator was not happy that his important advice was [[MemeticMutation afterwards taken out of context]] -- this itself became an example of [[SelfDemonstratingArticle Murphy's Law in action]]. Given that the actual Murphy's Law is something different, we cover this mutation under FinaglesLaw [[note]]A name created to give a proper name to the more common derivation[[/note]] instead. However, on this wiki, it references quite a few things, so we've made this page to help people figure out which one they really want.

Arthur Bloch's 1977 book ''Murphy's Law, and Other Reasons Why Things Go WRONG'' [[TropeCodifier popularized the term]], if only mostly with the above deviation. The first sequel, ''Murphy's Law Book Two'', disseminated HanlonsRazor, which is often a good explanation for why the wrong way was employed.

Another way of looking at this law is the '50-50-90 Rule', which is described as 'If there is a 50-50 chance, 90% of the time it will go wrong'.

If you want...
* ...the trope "Anything that can go wrong, will go wrong", it's under FinaglesLaw.
* ...the webcomic, it's under Webcomic/MurphysLaw, or possibly, ''ComicStrip/PVTMurphysLaw''.
* ...the trope about a bed that traps people, it's MurphysBed.
* ...the UK drama series with James Nesbitt, it's ''Series/MurphysLaw''.
* ...the law as laid down by Alex Murphy, that's Franchise/{{RoboCop}}.
* ...the show about Edward Murphy's optimistic, fictional descendant, it's ''WesternAnimation/MiloMurphysLaw''.

Also, Murphy was an optimist.