Only the disciplined mind can see reality, Winston. You believe that reality is something objective, external, existing in its own right. You also believe that the nature of reality is self-evident. When you delude yourself into thinking that you see something, you assume that everyone else sees the same thing as you. But I tell you, Winston, that reality is not external.
Reality exists in the human mind, and nowhere else.
Whatever the Party holds to be truth, is truth. It is impossible to see reality except by looking through the eyes of the Party. That is the fact that you have got to relearn, Winston. It needs an act of self-destruction, an effort of the will. You must humble yourself before you can become sane.