"The world of solitary confinement is a universe of its own...the isolation...the silence...the interrogations that would go on for 24 or 48 hours with no rest no sleep no food...the psychological...the minutes of silence and solitary routine stretched out without end...
There was no such sort of human companionship to sustain you at Lubianka. When you came back from an interrogation session here, you were on your own. You could only torture yourself by going over and over the session in your own mind, wondering whether what you had said was right, or what you might have done better, agonizing again and again over every question and every answer. Here there was no relief to be sought by talking it over with somebody else, by asking advice (poor as it might prove to be), by sharing experiences and sympathizing with one another.
Solitary confinement, in short, must be very much like what some theologians paint as the principal torment of hell: the soul at last recognizing its mistakes for what they were and condemned forever to the loss of heaven, constantly tormenting itself with reproaches and tearing itself apart because it still sees and understands and wants the things it has lost forever, but knows it is condemned to lose forever because of its own choices, its own failings, its own mistakes..."
From Walter J. Ciszek's book He Leadeth me