Murphy's Law
Sod's Law · Finagle's Law
The observation that if something can go wrong, it eventually will. A reminder to design for failure and plan for the unexpected rather than assuming the best case.
Origin
Named after Edward Murphy, an American aerospace engineer, during USAF project MX981 at what is now Edwards Air Force Base in 1949. When an assistant wired strain gauge sensors backwards during a rocket-sled test of human g-force tolerance, Murphy remarked that if there was a way to do it wrong, someone would. Colonel John Stapp — the test subject who survived 46 g's — rephrased and popularized the adage at a press conference, and the simplified "Murphy's Law" quickly entered popular culture.
Everyday Use
The one day you leave your umbrella at home is the day it pours. The toast lands butter-side down. Murphy's Law isn't just fatalism — at its heart, it's a design principle: if a cable can be plugged in backwards, someone eventually will, so design the connector so it only fits one way. The best engineers take Murphy's Law as a challenge, not a complaint.