Murphy's laws

things will go wrong in any given situation, if you give them a chance.

Finagle's Law of Dynamic Negatives (also known as Finagle's corollary to Murphy's Law) is usually rendered:

Anything that can go wrong, will—at the worst possible moment

Sod's Law is a name for the axiom "Anything that can go wrong, will".

Kaufman's Theorem of Interconnectedness - Any two items that can become entangled will become entangled.