Shooting a gun is not very difficult, though shooting one well has never been that easy. Not unlike many other things. Today, it is easier to learn than ever before, but still, people are people. The number one issue that needs to be overcome in order to shoot well at all, is the flinch.
I am clearly talking about the most basic of shooting ability, but if you do not overcome your flinch, no real progress can be made. Due to physiology, temperament, effort, desire, or the phases of the moon, some people are just not able to overcome their flinch. Others seem to some of the time but not enough of the time. I am convinced that if they put in more effort, most would overcome their flinch, though keeping that ability will likely take regular maintenance.
A small percentage of people are probably incapable of overcoming their flinch, but that is not usually true of anyone who is really motivated. The easiest and fastest way to get past flinching is with a .22LR. The lack of a .22 is one reason why so many professional gun toters never get good. Even with a .22, some people will still flinch. For those people, maybe golf is the way to go. If you prefer to shoot than to play golf, OVERCOME YOUR FLINCH! It is really that simple. Just decide to not move the gun while releasing the sear. It is literally mind over matter discipline, nothing more nothing less.

