If you've heard it once, no doubt you've heard it a million times.
Extraordinary claims require extraordinary proof.
That old saw has become the skeptic's number one attack against claims that threaten to overturn their cherished applecarts. As the arguments fly over what exactly constitutes the necessary proof, there's often some hasty rewriting of the rules of the game. For the would-be extraordinary, for the unorthodox claim on the verge of scientific success, the ground rules are gratefully changed. The phrase evokes an image of the goal posts in, say the endzone of a football game, that are slowly moved to the back of the endzone, or beyond, as one team threatens to score. The other team resorts to cheating by changing the rules of the game in an all out effort to prevent a loss.