I was absolutely amazed at how well soldiers actually performed in the presence of multiple traumatic injuries. I was personally on the scene of several mass casualty events just after they occurred - with the wounded and with those who responded to the attacks. The professionalism of the the first responders (the soldiers on the scene), the medics and the NCO and officer leadership was astounding. There was no panic. Training (and courage) kicked in and people did what they were supposed to do. The courage of the severely wounded and dying was even more inspring. I heard similar stories (and ONLY similar stories) from my friends in other units.
Before the war, as we trained to care for our wounded, I told some soldiers, "If you feel like you're going to throw up, just step to the side, throw up and then get back to the mission. There's no shame in getting sick - it's a normal reaction - just get back in the game because lives are depending on it." In fact, no one I saw did get sick during a crisis - even while they were walking around picking up body parts. There's something that about the crisis of combat that makes you (at least temporarily) very focused.
The training takes over and then they are amazed at how well they actually performed.