This is because “stand your ground” simply means that, if you reasonably believe that you face imminent death, serious bodily injury, rape, kidnapping, or (in most states) robbery, you can use deadly force against the assailant, even if you have a perfectly safe avenue of retreat. In non-stand-your-ground states, when you face such threats outside your home (and, in some states, your business), you can only use deadly force against the assailant if you lack a perfectly safe avenue of retreat. In no states are you allowed to shoot someone who is simply shouting at you or moving towards you loudly and aggressively, unless you reasonably believe that you’re in danger of death, serious bodily injury, or the other harms I listed. (When the person is coming into your home, in many states you can indeed shoot, but that doesn’t apply to confrontations on the public street.)
2. What if you just feel fearful for your life, but it’s not reasonable for you to feel such fear (again, of death, serious bodily injury, etc.), and you shoot and kill the person you fear? In some states, that would still be murder; in others, it will still be a crime, but a lesser one, usually called involuntary manslaughter or negligent homicide. But of course if your fear is unreasonable, a jury might conclude that it was insincere, too (even given that the prosecution must disprove your defense beyond a reasonable doubt, in all states but Ohio).
3. The stand-your-ground vs. duty-to-retreat distinction comes up in the relatively unusual case in which you are faced with a threat of death, serious bodily injury, etc., but you can escape with perfect safety. If you’re facing an assailant with a gun, it generally doesn’t matter what state you’re in, because you generally can’t escape a gun with perfect safety. So if you’re in the fortunately very rare scenario in which you reasonably believe that the person outside the clinic will imminently shoot you, you can shoot him in any state (if you’ve got a gun, that is). And if you’re in the much more common scenario in which you just think the person might slap you or block your entrance or insult you, you can’t shoot him in any state. Only in the very rare scenario in which you think the person might kill or seriously injure you, but with a deadly weapon that you can flee with perfect safety would it matter whether you’re in a stand-your-ground state or a duty-to-retreat state.
4. In Florida, the “stand your ground” principle is also used to refer to certain statutory procedural protections that are provided to people who claim reasonable self-defense; the cases against them can be dismissed at an early pretrial stage, if the judge concludes that they were likely innocent. That’s an important procedural protection, but it doesn’t affect the substantive rules I describe here.