In a fight, your adversary won't present you with an ideal target.
While competitions and most shooting courses reward center-mass shots, the ability to be able to hit just a portion of a threat—an arm, a leg—can be critical to prevailing in a gunfight.
In using a handgun in self-defense, every instructor of any worth teaches that your goal is to be able to fire, on demand, a well-placed--most times high-center-chest--hit. We collectively practice developing, and then maintaining, this ability.
Handgun competitions are built around how well a competitor does this. This ability is then often coupled with tactical considerations of concealment, cover and movement.
Little if any thought or effort, though, is devoted to learning to "shoot what you can see when you can see it," so to speak. In fact, all the competitions penalize the shooter for firing what is, correctly by the rules, a poor shot.
However, a problem can arise when forced to defend yourself because threats do not conveniently present themselves as a full-value, broadside target. But because all your training, practice and competition has habituated you to always attempt to position yourself to get a good hit, you will most likely do this instinctively when engaging a real adversary.
The "cure" for this problem, luckily, is not all that complex. Recognizing that what you are doing in one application is incorrect for the other is almost the solution in and of itself. To reinforce this, practicing shooting at a humanoid target's extremities--its "edges," if you will--can further imprint this difference.
I suggest using realistic human silhouette targets, if possible, to better imprint in your mind what you'll see in a real encounter.
You can position the target behind a sheet of opaque material to further enhance this visual imprinting. You can also blade your target so you can only see and shoot a small portion of it. The only downsides are some long bullet tears on the target and shot-up target supports. (Be sure to use wood, not metal, clips.)
If you want further testing of this skill, you can do so (to some extent) in an International Defensive Pistol Association shooting contest, where using cover is included in many of the courses of fire. Just decide you are going to go through the course of fire using as much cover as you can, not the minimum allowable without penalty.
The applicable rules requires that the contestant have 100 percent of the lower torso and 50 percent or more of the upper torso behind cover while shooting or reloading. There is no rule against using more cover if you choose. Your final score may suffer, since scoring is time-based, but the idea is to learn and test a skill--not win a match.
Obviously, you can't deliberately shoot target extremities in a match, though, as doing so can well ruin both targets and their supports. You won't get to finish the match or be invited back.
What I've found for myself is if I start the match with the intent of shooting stages in the most tactical manner and do this a few times, it becomes much more reflexive and my final score is not all that much lower. So if you can convince yourself to do this, rather than try to win, you are well on your way to having better skills in a real encounter.
Which brings us back to the advice in the beginning of this column: Shoot what you can see when you can see it. Which means any limb or portion of the body that is visible (and a proven threat, of course). You can then move to shoot more of the threat or not, but you have delivered the first blow.