It is only prudent never to place complete confidence in that by which we have even once been deceived. - René Descartes

[I]t seems to be just as foolish to say, 'I imagine, in order to understand more clearly what I am,' as to say, 'I am now clearly awake and I see something true, but because I do not yet see it clearly enough I shall fall asleep so that my dreams will represent it to me more truly and clearly.

Cogito ergo sum

Some people would deny the existence of such a powerful God rather than believe that everything else is uncertain. Let us grant them – for purposes of argument – that there is no God, and theology is fiction. On their view, then, I am a product of fate or chance or a long chain of causes and effects. But the less powerful they make my original cause, the more likely it is that I am so imperfect as to be deceived all the time – because deception and error seem to be imperfections.