Let us not forget rapid breathing and heartbeat, and adrenaline, and a host of other physiological factors that do not occur on a rifle or pistol range. They are very real when confronting a living creature be it animal or man. Hunters experience them to one degree or another, as do the military and law enforcement personnel. As I said earlier, it is an awesome responsibility.
Great point, Dave! You will do, under stress, what you do in training. High-stress leads to loss of fine motor skills - that's why we train to shoot "center mass." Much more likely to hit your target. You always hear the Monday morning quarterbacks asking why the police had to
shoot to kill; They have no idea "why" the officer is firing in the first place! When an encounter elevates to use of lethal force, it usually occurs at very short range, in a very short period of time. Anyone who tries to breath, aim at an arm or leg, then finely-place that shot, will not live to see another day. Practice, center-mass, and muscle memory is what will save you in a high-stress encounter.
Police are never trained to "shoot to wound," they are trained to stop the threat. A wounded suspect, who has already shown intent to take your life or the life of another, can still shoot back. Shoot until the threat is no more.