Ein langes Zitat, aber es scheint mir den Nagel auf den Kopf zu treffen:

Now, of course, this is probably just ordinary academic uncertainty. Yet from the perspective of the philosophy of science, this seems like the beginning of what Karl Popper and Hans Albert, philosophers who emphasized the importance of rational criticism of theories, called an “immunizing strategy.” (See Karl R. Popper, The Logic of Scientific Discovery, Chapter. 1.)

For example, suppose the fiscal stimulus policy is perceived to have failed. Has the theory been refuted? “No” will be the likely answer because the stimulus was not large enough. But if we are indeed out of the realm of the available evidence then such a statement is purely ad hoc – a fancy term for an expedient intellectual invention. Today’s Keynesians are getting nervous. They are either at the threshold of their greatest victory or at the precipice of their greatest failure. They want to be prepared for either.

Mario Rizzo in seinem Weblog, ThinkMarkets.