From a blog entry about psychiatry:
“When Marco Polo saw the exotic one horned quadruped, his frame of reference required that it could be none other than a unicorn, even though it did not conform exactly to his prior conception of it. Marco Polo made his observation fit his existing paradigm of zoology. While superficially (and in retrospect) this may seem silly and arbitrary, it is in fact the opposite, Marco Polo believed the only thing he could believe—because the alternative was to believe he had discovered an entirely new, unheard of, creature.“
While the original post dealt with psychiatry directly, I think there is a wider lesson to be learned here. Our assumptions about knowledge and authority can lead us down the wrong path.