A wise person uses force only as a last resort, only when it is the only remaining "safe" action
If you have ever read or skimmed the book
Self Defense Laws in All 50 States (
http://www.amazon.com/Self-Defense-...191&sr=8-1&keywords=self+defense+in+50+states) you will quickly learn that while there is quite a commonality in self defense laws, they are still enough different from state to state that you might get arrested in one state, but not another. It also depends on the culture whether or not you get arrested, prosecuted, and found guilty or not guilty. One state actually says that you have to retreat in your own house
I would try to retreat in daylight where I can see, but not at night and not if someone is breaking in the door or window at any time. But contrary to Biden, you can't shoot through the door, nor should you.
Many, or maybe most, states have some form of castle doctrine even if they don't explicitly say so. In NY State, the burden of proof for self-defense in the home is on the prosecution. In Western NY two people were acquitted after self defense incidents that I was very surprised got off, i.e., they could have avoided the whole situation.
So after reading this book I decided that the best approach is to always try to retreat. Never try to protect property. Do not intercede in a situation if you don't know how it started because if you shoot one person and it was the other that started the fight, you cannot call it self defense. I think stopping a rape is OK. Stopping a felony may be legal, but that varies from state to state. Stopping an arson on a building is often a named felony where you can shoot the arsonist.
IOW, the lowest common denominator action is the safest bet: Be able to show that you did everything you did to avoid shooting, but once you are really in danger of GBHoD (grievous bodily harm or death) shoot until they stop. In many cases that means showing your gun and they run. Which is where it gets tricky because you really can't wait to pull the trigger to see if they run.
The problem is that everyone but you is playing Monday morning quarterback with 20/20 hindsight.