But in real life things are often not that clear cut.
Consider the Arizona case of Harold Fish who was attacked by a man apparently unarmed, but was younger and bigger than Fish. Fish's attacker came charging at full tilt downhill toward Fish shouting he was going to kill him [Fish]. Fish, in fear of his life, shot and killed his attacker. He was convicted of manslaughter by a jury and sent to prison. He did win his appeal and is now free. But his judgment that he needed to use lethal force was certainly second guessed by the prosecutor and then the jury.
Consider another Arizona case, that of Larry Hickey. The charges have finally been dismissed, but he had to undergo two trials, with two hung juries, before he got off the hook (
http://www.examiner.com/x-18115-Coc...a-County-Superior-Court-dismissed-all-charges).
We all know that "a good shoot is a good shoot." The problem is that you’re not the one who gets to decide if it’s a good shoot.
If you’re involved in an incident and expect to claim it was self defense, whether your use of force was justified will be decided by others. First, the investigating officers will form an opinion. Then the question will be considered by the local prosecutor’s office, and then maybe by a grand jury. If you’re really unlucky, it will finally be up to a judge and a trial jury to decide if it was a “good shoot.”
So maybe the evidence was clear that you were acting in justified self defense. But then again maybe not. Maybe there are no witnesses, or the witnesses tell conflicting or equivocal stories. Maybe the only witness is the nice gentleman you happened to shoot, and his story is that he had the knife out to cut some salamis for a snack. Maybe the physical evidence isn’t clear one way or the other.
So maybe a lot is going to depend on your story and what the cops, DA, grand jury, et al think of you and your story. And a number of things can affect what those folks think of you and your story. One thing that can affect what those folks think of you and your story will be whether your judgment may have been impaired by alcohol or some other substance, even a prescription or over-the-counter, legal drug.
Be that as it may, anything that might have impaired your judgment could become an issue in a self defense case. That's just real life. Whether one leaves his gun at home is a decision he has to make.
But what if that's not what happens to you. What if what happens to you is that you're accosted on a deserted street by a man with his hand under his coat and telling you he has a knife and is going to cut you up if you don't give him your wallet and that he just might cut you up anyway? You believe him. He starts towards you, and you shoot. When the smoke clears, you find that you had shot an unarmed man; he was just bluffing about the knife.
You can't know what's going to happen.