It becomes easy to spread a lie when no one knows what the truth is. - anonymous
If no one knows what the truth is, how can it be a lie?? For instance, if I said "the sky is red", and everyone is blind, then just because no one can verify the color of the sky doesn't make what I said a lie.
When the religious right tells everyone what Jesus would think and do and most people don't read the bible to find out for themselves what the book actually says then most people won't know they are being lied to. Similarly, if the NSA says "We've stopped spying on US citizens" and then classifies all NSA activity as top secret then the public will know whether or not they are being lied to. If a husband says to his wife, "I have never cheated on you" and the wife is blissfully ignorant of the truth then it is still a lie. Technically, yes, someone (the husband and the other woman) know the truth, so instead of literally interpreting the words consider the meaning.
It is the custom of each community to form the minds of its young in a mold, introducing a binding agent of prejudice. The result is a remarkably tough substance capable of withstanding successfully even the pressure of many innate tendencies and instincts. In this way it has been possible to produce a man who against all his basic sense of self-preservation will voluntarily risk death for an ideal - but also in this way is produced the dolt who is sure of everything and knows what is 'right'.