I used to doubt the validity of people claiming they were unaffected by the pain of a groin strike. In fact, I knew of a TKD practioner who was telling people that at his school they trained to ignore the pain, which always made me wonder exactly what such training could consist of, and tempted me to ask if I could test his claims. However, after training for several years and getting hit many times, I would say that while it's still incredibly painful, I can often ignore the pain and continue what I'm doing. For instance, I've been hit while teaching classes and continued teaching without reacting to the pain so that the student wouldn't feel self conscious. I've also been hit while training in street clothes and just shrugged it off. It's not that it didn't hurt. It hurt. I just put it aside and continued with what I was doing. Of course I think this also has to do with the degree of force applied. The soft kill hurts, but I think we can generally ignore it if we try. If someone were to grab, squeeze, and twist? I think I'd probably pray that I passed out before I died.
I don't mean to sound like I'm bragging by any stretch, and in fact, I'm still irritated by the guys who act like they could take a sledge to the stones and smile, but I think that with proper focus you can keep it from stopping you. None the less, you still notice it, and that distraction might be enough to create an additional opening. I still train and use groin strikes, but I feel that I'm more aware of their potential now. To me, this is similar to eye strikes. I used to think these were devestating, but I've been hit in the eye many times and continued fighting, even if I had to close one or both eyes. I saw one of our instructors take a finger two inches into the eye on accident, and he was able to shrug it off because it slid around the eye and didn't cause any damage to the eye itself. Again, I'll poke a person in the eye, but I don't put all my money on that strike winning the fight.
-Rob