Ability, Opportunity, Jeopardy--- Elements of Lawful Self-Defense

There is an excellent article at a blog called Cornered Cat, A Woman's Guide To Concealed Carry. The article, "Can I shoot him? Ability, Opportunity, Jeopardy" goes into the three elements each of which must be present for a valid self-defense claim: did the attacker have the ability to cause serious physical harm or death? Did they have the opportunity to inflict that harm? Did they act in such a way that a reasonable person would believe they intended to cause serious physical harm or death? These three elements are applicable in every state, regardless of whether you are under Castle Doctrine or Stand-Your-Ground laws. Specific laws might make it easier or harder for you to prove one of these elements, but the basic principles stay the same. Know the principles, and it gives you a basis to evaluate what changes in the laws might mean or what might happen under the laws of different states you travel through.
For example, under Missouri's Castle Doctrine, you may presume that a person invading your home in the middle of the night intends harm. The same goes for the victim of a car-jacking in Missouri: it is reasonable to assume that a car-jacker is not mistaken about where they parked. That makes it easier for a homeowner or a driver to show jeopardy in those circumstances. If you encounter an intruder in your pasture in the middle of the night and you cannot tell what they have in their hand, it may be reasonable for you to assume that they have the ability to cause serious physical harm or death, but you still must demonstrate opportunity and jeopardy--- and you probably cannot do that if you shoot them while they are running away.
In any case, I recommend reading the article, and especially if you are a woman concealed carrying, you may want to dig through the other useful materials on the Cornered Cat.