"With all great deceivers there is a noteworthy occurence to which they owe their power. In the actual act of deception, with all its preparations, its enthralling in voice, expression and gesture, in the midst of the scenery designed to give effect, they are overcome by belief in themselves: it is this which then speaks so miraculously and compellingly to those who surround them. The founders of religions are distinguished from this great deceivers by the fact that they never emerge from this state of self-deception: or very rarely they experience for once that moment of clarity when doubt overcomes them; usually, however, they comfort themselves by ascribing these moments of clarity to the evil antagonist. Self-deception has to exist if a grand effect is to be produced. For men believe in the truth of that which is plainly strongly believed."

Someone recently quoted from Nietzsche. This is another one from the same source.