[Zak]

Self defense with a firearm can be part of a plan to avoid being the victim of violence, but it works a lot better in a society where crime is rare, serious crimes are likely to be punished, and the probability of profiting from major crimes is low. When skilled and motivated criminals attack unsuspecting victims, they tend to be successful even if the victims are armed.

Case in point, in 1986, Michael Lee Platt and William Russel Matix went on a crime spree in the Miami area. They started by murdering a man at a shooting range to steal his firearm and car. They then tried and failed to rob an armored car, murdering an armed guard in the process. Next, they robbed a bank. After a couple months off, they robbed another armored car, during which they stole a guard's rifle and murdered him with it. A couple months after that, they robbed and attempted to kill another man at a shooting range, using his stolen car in a bank robbery a week later.

All of the victims these criminals shot were armed, which did not dissuade them from initiating attacks. The armored truck guards were presumably trained, but not sufficiently to defend against attackers whose opening move was gunfire.

https://en.wikipedia.org/wiki/1986_FBI_Miami_shootout