http://tvtropes.org/pmwiki/pmwiki.php/Main/MurphysLaw

Meredith Grey, Grey's Anatomy "It Only Gets Much Worse" "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."

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

As originally applied, Murphy's Law — coined by, and named after, U.S. Air Force engineer 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 Idiot-Proofing or "defensive design". For instance, the loss of several F-111 (TFX) aircraft during the Vietnam War happened 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 "If there is any way to do it wrong, [the technician] will [achieve it]".

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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 afterwards taken out of context — this itself became an example of Murphy's Law in action. Given that the actual Murphy's Law is something different, we cover this mutation under Finagle's Law note A name created to give a proper name to the more common derivation 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 popularized the term, if only mostly with the above deviation. The first sequel, Murphy's Law Book Two, disseminated Hanlon's Razor, which is often a good explanation for why the wrong way was employed.

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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'.

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Also, Murphy was an optimist.