It doesn’t take much to be proficient at getting a gun out and ready. Plus if you’re paying attention to your surroundings many times there are clues something is going to happen and you could potentially be ready. Also many times, such as in business robberies the robbers attention is divided which provides opportunities to respond.
As far as defending yourself over property, if someone points a gun or a threatens me with a knife the only logical assumption is that they are willing to use it to hurt me. There are many cases of robbers killing people in cold blood after they’ve done everything asked of them by the robber. I’m not going to put my life in the hands of a someone who is threatening to kill me, so if given the opportunity armed or not I will defend myself. As should you.