the way in which plans always fail and bad things always happen where there is any possibility of them doing so I'm a great believer in Murphy's law - what can go wrong will go wrong.
If anything can go wrong, it will, as in We may think we've covered all the details for the benefit, but remember Murphy's law . The identity of Murphy, if ever a real person, is unknown. Some think it alludes to (but was not invented by) a feckless Irishman named Murphy. [c. 1940]