Something we teach in all of our courses is practice the way you want to perform under duress. If you get into a situation where you need to use your handgun, your adrenaline will be pumping and you won't be thinking. What will you be doing? Your body will automatically be performing what you've trained it to do - a common term for this is "muscle memory."
For example, when you train, how many shots do you fire in a single string? If you step to the line and shoot until the slide locks open on an empty magazine - that is likely what you will do in a self-defense situation.
For example, see the Dashcam video of Chicago police shooting Laquan McDonald in late 2014. Mr. McDonald was shot 16 times by one police officer.
I am not discussing whether or not the shooting was justified. Mr. McDonald had a knife and was clearly disregarding the commands from the police. Since we weren't there it is hard to judge what made the officer decide to shoot.
If you watch carefully you can see small puffs of smoke coming from Mr. McDonald's body after he falls to the ground. I would guess he was shot at least 8 times after he was on the ground. No one would argue that Mr. McDonald was still a threat to the officers on the ground. Shooting him on the ground was likely not intentional by the police officer. I believe that he probably trained by doing a magazine dump when shooting his pistol. Thus, when he needed his gun against a real target he shot until the gun locked open and hit his target 16 times. We train to shoot twice at the target and then evaluate if the bad guy is still
You've heard the saying "practice makes perfect." For handgun training, think "perfect practice makes perfect."