Let's say you pull up to a convience store and you get out of your car/truck and approch the front door. After you scanned the parking lot for threats, you noticed that there is a hooded BG standing at the counter with a gun pointed at the clerk. The guy has not made eye contact with you, so your still unnoticed. How would you react?
It's better to have it and not need it, Than to need it and not have it