The model was coherent, dramatic, and well-supported by the evidence available through the 1970s.

The model also had powerful institutional defenders.

Several of the most respected researchers in American archaeology built careers on it and were not inclined to see it overturned without extraordinarily compelling evidence.

The standard for acceptance of pre-Clovis claims was accordingly high — as it should be for extraordinary claims — and many proposed pre-Clovis sites were found, on close examination, to have chronological problems or contextual ambiguities that undermined their claims.

This created a situation that critics called a self-fulfilling standard: the threshold for accepting pre-Clovis evidence was set so high that sites with genuine but imperfect evidence were dismissed, while sites with perfect evidence remained elusive because perfect preservation is rare.