Burden of Proof
Time and time again, the concept of 'burden of proof' comes up in a debate. Many people who have no evidence to back up there beliefs, aside from personal anecdote, will pull out the "well you can't prove me wrong!" debate. This is a logical fallacy because of the burden of proof lies on the person making the claim...not the person who disbelieves said claim...and the main reason why a site rule is to not present beliefs as facts (unless you have the concrete evidence to back it up).
Here's a great video explaining the concept of Burden of Proof:
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"All that is gold does not glitter, not all those who wander are lost."-Tolkien
"All that we see or seem is but a dream within a dream."-Poe