The more I think about it, the more impressed I am by Barry Boehm's willingness to disavow the "spiral development model" he created - not because he came up with a better theory or found a flaw in the documentation, but because nobody could actually do it correctly.
Some people might have just blamed all those dumb practitioners, those silly program managers who don't know what they're doing and should have listened harder, tried harder, studied harder, and generally done things better. But Mr. Boehm recognized that a smart-sounding theory which can't be implemented isn't actually worth very much.
That's a remarkable demonstration of integrity and humility.
Now, it might be an apocryphal story. A professor has mentioned it in class a few times, but I haven't found any references to it online. I do hope it's true...