CS Lewis

The more a man was in the Devil's power, the less he would be aware of it, on the principle that a man is still fairly sober as long as he knows he's drunk. It is the people who are fully awake and trying hard to be good who would be most aware of the Devil. It is when you start arming against Hitler that you first realize your country is full of Nazi agents. Of course, they don't want you to believe in the Devil. If devils exist, their first aim is to give you an anesthetic—to put you off your guard. Only if that fails, do you become aware of them.