Here is the way most people should look at this.
I know what I am capable of. Very little. Bad shoulder, bad knees, and too many years without lifting weights. On the one hand, I know that I could take the initiative, and put down a person bare handed, even one far larger than I am, because I know some combat skills. I have enough strength, enough training, and reflexes and balance that can carry me through a quick takedown.
Anyone who gets into my face and threatens me, If I believe he is serious, is going down. I will not give him the opportunity to strike first. I don't have to. I have been threatened with violence,and if I don't see a clear path of avoiding it, I will take the fight to the enemy.
My enemy, obviously, will have underestimated me, if he thought I would submit to attack without fighting back.
OTOH, do I dare underestimate him? Not at all. When I am seriously in fear for my safety, when all else fails, I am going to go all out, and do everything possible to disable him.
An unarmed opponent is the worst situation to be in when you are an older, or more fragile person, and carrying a weapon. Will you exercise lethal force when you need to, or will you withold the use of your weapon until it is too late, because it felt wrong shooting a guy who just punched you?
If you are attacked or accosted, it is your duty to yourself to consider a worst case scenario. You have to assume that the guy who has been watching you from across the bar, and just came over and poured beer on your shoes is just as dangerous as a rabid pit bull. Unless you are absolutely confident that you can stop him otherwise, go straight to threat of lethal force and follow through with that threat.
many, many people have died or gone through life altering events because they underestimated the threat an assailant posed. They did not respond properly.
Kinda disjointed there, and I didn't really do a great job saying it, but in summary, NEVER UNDERESTIMATE HOW POWERFUL, VICIOUS, ANGRY, OR DETERMINED TO HURT YOU YOUR ASSAILANT MIGHT BE. If someone has just accosted you in a parking lot and calls you evil, it may be a simple matter of walking away, but in the next second, you may be fighting for your very life against a psychotic who thinks you are satan.