Finagle's Law n.
The generalized or `folk' version of Murphy's Law, fully named "Finagle's Law of Dynamic Negatives" and usually rendered "Anything that can go wrong, will". May have been first published by Francis P. Chisholm in his 1963 essay "The Chisholm Effect", later reprinted in the classic anthology "A Stress Analysis Of A Strapless Evening Gown: And Other Essays For A Scientific Eye" (Robert Baker ed, Prentice-Hall, ISBN 0-13-852608-7).
The label `Finagle's Law' was popularized by SF author Larry Niven in several stories depicting a frontier culture of asteroid miners; this `Belter' culture professed a religion and/or running joke involving the worship of the dread god Finagle and his mad prophet Murphy. Some technical and scientific cultures (e.g., paleontologists) know it under the name `Sod's Law'; this usage may be more common in Great Britain.
One variant favored among hackers is "The perversity of the Universe tends towards a maximum"; Niven specifically referred to this as O'Toole's Corollary of Finagle's Law. See also Hanlon's Razor.