The normal human reflex to pain is not to resist what is causing the pain but to get away from what is causing the pain.
When someone applies sankyo to you do you resist or move to avoid the pain? I avoid the pain.
I might not be normal..
. but I actually had to be trained and often have to be reminded to move to avoid the pain in sankyo. Before I began to learn to move, I would not move even when a pin or lock hurt a great deal. In one instance when I was first learning someone was doing kotegaeshi and I would not go down. He said to me "I can make it hurt". And I looked up and said ,"you already are making it hurt.....You don't have my center." Now I know not too bright on my part but I was also not intentionally resisting I just felt no real reason to move, its just how my brain appears to be wired and I had not yet really come to understand how to be a good uke. But of someone gets my center and unbalances me right I'll go down like a sack of bricks. And generally get the "how the heck did I get down here?" feeling right before I start to laugh. When that happens I rarely feel a bit of pain or discomfort.