The Uncertainty Theorem: A Mathematical Proof of the Obvious, by Alberto P. Obviousius

It is well-known that everything is uncertain, except for the certainty of uncertainty itself. This theorem proves it.

Let x be a random variable, and let S(x) be the probability that x is certain. Then, by the Pigeonhole Principle of Uncertainty, S(x) = 0.5, because it's just as likely that x is certain as it is not.

Q.E.D.