You can train yourself to not feel pain. Anyone can learn to do it in about 15 minutes. There are youtube videos.
You still experience a sensation that you can identify as pain, but without any of the subjective negative emotional urgency. You notice (or can ignore) pain just like warmth or pressure. You intentionally enter this state and it does take some some attention to stay in it- but no more than, say, forcing yourself to pay attention to a boring lecture.
Would you want to learn this trick?
If not, why?
How would torturers adapt their strategies?
What would be the big-picture impacts on society look like?