1. Most of what you know is wrong.
2. Even what's right is only mostly right.
3. Part of the problem is the residue of half-facts and pseudofacts, the detritus of actual memory that becomes indistinguishable from truth in the cluttered mind.
4. Or, to use a different metaphor, from a grab-bag of anecdotes and factoids, you are likely to pluck something stale or half-eaten.
5. It's not whether you're wrong--because you probably are--but whether you are willing to intellectually clean house, or, again switching metaphors, pick that stale factoid out of your teeth.
For what it's worth, a slew of articles--this one in particular--punctured a myth I'd believed true, and prompted this post. As a teacher who loves an impromptu lecture, I've assembled a vast mental trivia collection, always ready to deploy a fact that might amplify a point I'm making. It hurts to be wrong, but it hurts more to be confidently, persuasively wrong in front of a class full of eager learners.
So I become my own Snopes.com, constantly fact-checking myself. And although the folks who run Snopes worry that extreme skepticism is harmful to knowledge, in my experience, in the grand scheme it's dwarfed by gullibility, intellectual laziness, and false confidence in fake facts.