But we also see evidentiary thresholds not being crossed—sometimes for centuries, as in the case of Pliny’s medical theories. As powerful as confirmation bias is, it cannot fully account for this: for the persistence and duration with which we sometimes fail to accept evidence that could alter our theories. Another factor is the claim, implicit or explicit in many belief systems, that attending to counterevidence can be dangerous—to your health or family or nation, to your moral fiber or your mortal soul. (As a European Communist once said in response to the question of whether he had read any
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