An interesting point on how what we believe changes over time. One of the more fascinating things about this book is how it makes good points about both the mutability of human belief and perception, and the universal truths and immutable beings that underlie religious thought. The latter have been postulated by humans, who are infamous for the former; how are we to trust such unreliable sources about issues this important? I'm not sure yet if Gene Wolfe answers, but he definitely gets you thinking.
It is said that it is the peculiar quality of time to conserve fact, and that it does so by rendering our past falsehoods true. So it was with me. I had lied in saying that I loved the guild - that I desired nothing but to remain in its embrace. Now I found those lies become truths. The life of a journeyman and even that of an apprentice seemed infinitely attractive. Not only because I was certain I was to die, but truly attractive in themselves, because I had lost them. I saw the brothers now from the viewpoint of a client, and so I saw them as powerful, the active principles of an inimical and nearly perfect machine.
Knowing that my case was hopeless, I learned in my own person what Master Malrubius had once impressed on me when I was a child: that hope is a psychological mechanism unaffected by external realities. I was young and adequately fed; I was permitted to sleep and therefore I hoped.
In this case, Severian's lie becomes true due to his changed situation. But there's another way for it to happen, I think, and that's just plain habit. This happens when you're lying to yourself, and you know it. But over time, if you're consistent in lying to yourself, the thought starts to come so quickly and naturally that it seems like the truth. Eventually you forget that it's a lie. And at that point, is it really a lie? If you think of any other ways we spin lies into truth, let me know.
The point about hope rings true with me, but if it is true, why would anyone commit suicide? Even people with lives that appear very successful have committed suicide. So I could make the statement that "despair is a psychological mechanism unaffected by external realities."