You know how some religious people are so silly
that they actually think anyone who disagrees
with them must be the devil in disguise? How
preposterous is that? They actually think there’s
an invisible guy lurking around trying to trick
them. See, they know the devil exists because
there always seems to be someone trying to trick
them, so it must be the devil because that’s what
the devil does – tries to trick people, and that’s
how they know he exists. If you point out that this
is circular logic, they don’t understand you, and
so they think you’re trying to trick them and
therefore you must be the devil. You have to ask
yourself how these people are able to walk and
talk at the same time.

Professor Poetry Hound

http://www.poemhunter.com/poem/walking-in-circles/