O’Brien is explaining to Winston that reality is only what you believe it is and the Party only wants members to believe the collective reality. O’Brien also tells Winston:
We control matter because we control the mind. Reality is inside the skull. You will learn-by degrees, Winston. There is nothing that we could not do. Invisibility, levitation-anything. I could float off this floor like a soap bubble if I wished to. I do not wish to, because the Party does not wish it. You must get rid of those nineteenth century ideas about the laws of nature. We make the laws of nature. (Page 264-265).
The Party feels that if they have the power to control someone’s mind they have complete control over their life. Another control technique is hopelessness; the Party assures its members that even if you die the Party never will, you mean nothing to the Party, you are