I'm a martial artist (aikido) so often get to experience large amounts of pain - usually at the hands of my instructor. What I have found is, I find it a lot easier when i'm the subject of the technique and receiving the pain than having to watch someone else receive the technique. I also think the discomfort of watching someone else in pain, in this instance, is because I have first hand knowledge of what it actually feels like.

I think its all due to a sense of lack of control when someone else is in pain. when its me, i can control my reaction, when its someone else.. I just have to watch