Finagle's law of dynamic negatives (also known as Melody's law, Sod's Law or Finagle's corollary to Murphy's law) is usually rendered as "Anything that can go wrong, will—at the worst possible moment."
The term "Finagle's law" was first used by John W. Campbell Jr., the influential editor of Astounding Science Fiction (later Analog). He used it frequently in his editorials for many years in the 1940s to 1960s,[1] but it never came into general usage the way Murphy's law has.