Don't accept the post or stay unless you have an understanding with the President that you're free to tell him what you think "with the bark off" and you have the courage to do it.
Donald RumsfeldThere's another way to phrase that and that is that the absence of evidence is not the evidence of absence. It is basically saying the same thing in a different way. Simply because you do not have evidence that something does exist does not mean that you have evidence that it doesn't exist.
Donald Rumsfeld