I like Happy's Explanation!! Great way to remember!!
Verb vs noun. I like Happy's answer.
However, it brings a story to mind. Professor Wolfgang Pauli is an immortal in the field of quantum physics for "the Pauli Principle" (and well you may ask what's the difference between principle and principal, whereupon I would refer you to my opening sentence).
What is less well known is "the Pauli Effect" which refers to the experiments which would go wrong if he was in the lab. For all his brilliance, the guy was a klutz, and if he was involved in lab work his colleagues had to be on guard against the likelihood of broken equipment.