Most of the time, torture fails due to the poor ability of the interrogators to craft the questions. In fact, that failure is the problem with most interrogations, torture or not.
The prisoner shouldn't be learning more from the questions than the interrogator is learning from the answers.
i.e.
"Where were you last night at 10PM" informs the prisoner that the interrogator wants to know about last night at 10pm. . . .
"When did you meet with the british embassy guard?" also giving away a lot here.
Of course, it's hard to get the information you want by looking stern and holding up a flash card with a "?" on it, which is the ideal. (Other than the fact that you are curious, you tell the prisoner nothing that way.).
In watching players "interrogate" people, 9 times out of 10 they are offering too much information, and also leading the discussion, offering loads of opportunities for the prisoner to lie.
In a tangible instance of actual fact, torture will probably work almost every time. . .for instance if someone stole a watch, and hid it in their apartment, and the owner grabbed them and tied them up 10' from where the watch is hidden and asked "Where is my watch?" and hit them with a hammer every minute they did't have their watch back, I'd say the odds are about 100% that they'll be leaving the place with the watch within an hour.
Saying "Torture doesn't work" is like "Violence never solves a problem". . .nice to think, but doesn't actually apply in real life.
The problems with torture are:
1) instances where you DON'T have my watch, and I refuse to beleive it.
2) Instances where I want to torture you, and the watch is just an excuse.
3) Instances where "The watch" is an intangable, like "Are you a rebel?"
4) Nothing can prove a negation. "I don't have your watch!" or "I am not a rebel!"
5) All the above combined with the leading issue from the top. . .if you keep asking about rebels and torturing someone, if they don't know any rebels, they'll start making stuff up.
"Torture" in it's bare outline, of "Do this/tell me this or I'll punish you" are the basis for a lot of life. . .like "If you don't like working here you can quit" or "Do this or you're fired" or "Stop running or I'll shoot". . . .they all work quite well. . .of course, they can all be used abusively, or used to create lies . . .coersion is not the ultimately most efficiant way to get what you want, but it's certainly one of the lazier ways, so you see it in effective use every day.