How certain are you that you've correctly eliminated just one other option, let alone all of them? Steven Kaas once said: "When you have eliminated the impossible, whatever remains is often more improbable than your having made a mistake in one of your impossibility proofs."

If that quote doesn't do it for you, check out http://www.gwern.net/The%20Existential%20Risk%20of%20Mathema... for an interesting post about mathematical error.