It is perfectly possible for a man to be out of prison, and yet not free - to be under no physical constraint and yet to be a psychological captive, compelled to think, feel and act as the representatives of the national state, or of some private interest within the nation, wants him to think, feel and act.

The nature of psychological compulsion is such that those who act under constraint remain under the impression that they are acting on their own initiative. The victim of mind-manipulation does not know that he is a victim. To him the walls of his prison are invisible, and he believes himself to be free. That he is not free is apparent only to other people. His servitude is strictly objective.
Brave New World Revisited, Aldous Huxley, 1958