The first precept was never to accept a thing as true until I knew it as such without a single doubt.
Rene DescartesWhatever I have up till now accepted as most true and assured I have gotten either from the senses or through the senses. But from time to time I have found that the senses deceive, and it is prudent never to trust completely those who have deceived us even once.
Rene Descartes