A story making the rounds illustrates the importance of ensuring that you have enough gun:
A large bull moose spent more than an hour stomping on the sled dog team of a rookie Iditarod musher in the wilds of Alaska last week – and the attack didn’t end even after Bridgett Watkins emptied her gun into the animal.
[…]
‘As he charged me I emptied my gun into him and he never stopped,’ she wrote on Facebook. ‘I ran for my life and prayed I was fast enough to not be killed in that moment. He trampled the team and then turned for us.’
[…]
She did carry a .380 caliber gun because there are few people where she trains, and she keeps it to to deter or scare off animals. She has since upgraded to a larger caliber firearm after it didn’t stop the moose.
A bull moose is basically a freight train on legs that is fueled by rage. Shooting one with a .380 will just piss it off. In Watson’s defense, she wasn’t foolish enough to believe that a .380 would drop a moose. She carried it assuming that the noise it created would be sufficient to scare off an attacking animal.
So this story illustrates two important consideration when creating a self-defense plan. First, recognize the threats and bring sufficient firepower to deal with those threats. Second, if your plan includes deterrence (which it should), have a backup plan in case it doesn’t work.
Consider the self-defense plan one might establish in a city. Your primary threat will likely be humans. That means calibers like 9mm, .45 ACP, 5.56x45mm, and 7.62x39mm are sufficient in most cases. Pepper spray is a non-lethal option that is often sufficient to dissuade an attacking human. In a city your defensive plan might include a 9mm handgun and a small canister of pepper spray.
Now consider the wilderness in the Upper Midwest. While humans are still a threat in the wilderness, they’re much less common in the wilderness and smaller than some other threats. If you go to the northern parts of Minnesota, you might encounter moose. Throughout much of the Upper Midwest there are also black bears. Both are larger than humans and require more firepower to reliably drop. Therefore, your self-defense strategy might include a .357 magnum, .44 magnum, or 12 gauge shotgun loaded with slugs. Run of the mill pepper spray won’t be sufficient, which is why bear mace exists. In the wilderness of the Upper Midwest your defensive plan might include a .44 magnum revolver and a canister of bear mace.
Obviously a gun and chemical irritant aren’t a complete self-defense plan. There are many other components including a plan to deal with injuries (which is even more critical in the wilderness where emergency services are often unavailable). However, like every other part of your plan, your lethal and non-lethal tools need to match the environment.