I'd say that at it's best, the pain is entierly unnessesary.
Hmm. If... and it's a BIG if... If you're "out there" and needing to do nikyo "for real" - you'll do whatever the heck is needed to put the other person down. In an "out there" situation, if we're even able to actually put a nikyo on someone in a real life-and-death fight, the purpose would be to break the arm and put the person out of action. We TRAIN to move either to avoid feeling the pain (wimps) or to tolerate some pain before complying because the body's all seized up due to the positioning. We don't train to break our partner's arms because we need to practice with someone and if we bust them up, we don't got nobody to practice with. In the "real world" whatever that is, attacks are nasty, aimed at killing, and we can't afford to give up anything in making "uke" comply... Bust the arm, take the knife away from him (usually - if we're lucky) and cut through the triceps and biceps so he can't use that arm any more - or shove the knife through the foramen magnum (in science class with frogs this is called "pithing"). THEN call for a lawyer to help stay out of prison.
All that, of course, happens (maybe) AFTER we've tried to talk the attacker out of fighting, After we've run away, and AFTER the SOB has caught up to us with foul intent. Or... because we've spent so much time forgetting that it's a MARTIAL art, we get ourselves stuck full of holes.
It's a MARTIAL ART ffs.