Something Else I've Learned Since Kindergarten

I can't believe I forgot this one on my initial list:

Occam's razor

"Pluralitas non est ponenda sine neccesitate" or "plurality should not be posited without necessity." Read more here at The Skeptic's Dictionary.

or, as Wikipedia describes it:

"entia non sunt multiplicanda praeter necessitatem", roughly translated as "entities must not be multiplied beyond necessity."