The mythical author of Murphy's Law:
If anything can go wrong, it will.
There's even a cottage industry around this law and other derivations - see, for instance, http://www.murphys-laws.com/ as one example.
One of my favorite corollaries is
If anything can't go wrong, it still will.
AM I am surprised by the above link: it does not mention Samuel Beckett's novel "Murphy" - I always took that as the origin of the "law".