"The fundamental problem with interrogating someone you have captured is that you have them entirely in your power but you still don't have access to the inside of their head. An idiot will solve this by getting a large stick or a knife or something and threatening to hit you with it. Then you will refuse to give them what they want out of principle. Then they'll hit you some more. Eventually the desire to cease being in pain will overcome principle and you'll tell them something, but it doesn't need to be the truth. This leads to two key problems. If they believe, for example, that your book records your heterodox cultivation techniques that they would also like to use, you can misinform them that the word 'not' in the sentence 'you should not channel qi into your eighth meridian or else your head will explode' means 'must' and then when they try and use the technique their head will explode. Secondly, if they believe that your book describes your cultivation techniques and in fact you've just been noting down everyone's name and description so you don't get embarrassed by forgetting, you have no way to convince them of that and will just get tortured forever or until you make up something that seems persuasive."
"If I were doing this, I firstly would choose to ask about information I could verify, like the location of hidden treasure or the passkey to a vault, rather than the translation of the text in a mysterious enchanted book. Secondly, I'd talk to you, discover what principles make you want to conceal this information from me and how they can be put in tension with your other beliefs, make sure you believe in the possibility of a future outside this cell if you cooperate, and in the mean time keep you hungry and sleep deprived and isolated and emotionally off balance so you're not in a good state of mind to actually refute any arguments. And then maybe if that didn't work I'd get someone else with a big stick to hurt you, but I'd be very apologetic about it. And I would let you go at the end, because my reputation matters too."