When asked why I carry three guns, I reply: "Because four would be ostentatious." In reality, the practical answer is less snide, but a bit longer to detail.
Many people, including those who carry guns every day, think that carrying multiple guns is overly paranoid. They argue that the chance of needing one gun is miniscule, the chance of needing two is even more so, and three is, well, off the charts.
My reason for carrying three guns is not that I think that I would necessarily need three guns in a gunfight, but to ensure having access to one gun when I need it the most. Much like the fighting adage: "Two is one and one is none."
They say that the more you know about gun fighting, the less you want to be in one. I would also add that the more you know about gun fighting, the more you know what techniques and equipment work, and what doesn't work. I follow the teachings of the great American philosopher, Clint Eastwood, who said: "A man has to know his limitations." In training, you learn the limitations of your physical abilities and capabilities and those of your gear.
My primary weapon is a Springfield Armory XD45. I prefer full-size guns because they make it easier to hit what I am aiming at and they carry lots of lead — in this case, 14 rounds of .45 ACP goodness. I also carry a spare magazine on my support side. I do this for two reasons: 1. Extra ammunition in case I need it. 2. Magazines are the weakest link in semiautomatic pistols, and they are the most likely culprit of malfunctions and jams. If my pistol goes down, more than likely it's magazine related. Having a spare gets the gun operational again.
For backup, my second is pocket carried — usually a snubby — accessible to my support hand because I know through study of both real and simulated gunfights, there is a strong probability of getting shot in the dominant hand or arm. In fights, adversaries focus on the threat, and in gunfights, that's the gun hand. With the eyes focused on the gun, the body, and thus, the aim point focuses there as well.
As a demonstration of the eyes and shots following a threat (the gun), take 10 shooters and have them shoot a generic target. Then, have them shoot a photo-realistic target depicting an attacker pointing a gun off to the side at them. You will see the groups drift towards the gun. The reason is that the mind and eyes concentrate on the threat, and the gun goes in the direction of the eyes. This happens even more intensely in a real fight. Secondly, most shooters hold their gun right in front of, and a little high of their center of mass, which coincidentally, is the place where most trained people aim. For this same reason, the primary gun itself can be disabled by being hit by a bullet.
Getting back to pocket carrying a snubby, I prefer internal hammered, or shrouded revolvers for pocket carry rather than a semiautomatic pistol because of the shape of the frame. Rather than a squared-backed semi, the rounded rear top of the revolver's frame makes it less likely to get caught in the pocket. Also, revolvers are less sensitive to pocket dirt and lint.
Another good reason for a backup gun is that the primary firearm can jam. This could happen for a multitude of reasons such as being rolled around in the dirt during a fight, broken firing pin/striker or simply a worn magazine spring. Additionally, guns, like all mechanical devices break, just because.
A backup gun is also important if your primary gun gets taken in a gun grab. Many altercations start as a physical, hand-to-hand fight. If the gun is inadvertently discovered during the tussle, it may be grabbed from you.
In a similar fashion, the gun may be taken from you if deployed at the wrong time. Example: If you are down on the ground fighting without proper control on your attacker's arms/hands and you reach for your gun, it opens you up for a gun grab. It's all well and good to say that you won't do that, but funny things tend to happen when you are fighting for your life.
Running out of ammo is a good possibility as well, especially when faced with multiple attackers. The FBI states that multiple attackers perpetrate nearly half of all violent crimes, and that percentage is increasing. Fourteen rounds may not be as convincing when faced with four attackers. Some folks prefer a New York Reload (changing guns) rather than reloading their primary weapon. For them, it is faster and presents a lower chance of fumbling and screwing up. This is important under the extreme stress of a life-threatening attack.
Don't forget the possibility of drugged up thugs, which are becoming more common. These attackers feel no pain and usually require numerous rounds on target to stop their body's locomotion.
If in a struggle, you are pinned, and either your primary weapon or strong hand is unavailable, a gun accessible to your support hand may be your savior.
My third gun, also a snubby, is on my ankle. I carry it there for two reasons. Through training, I know that a belt-borne firearm or pocket holster can be very difficult, if not impossible, to access if the fight goes to the ground - again a good likelihood. There are a few techniques that allow a draw from an ankle holster when your belt holster is unable to be reached. Ankle holsters are also very good for use in a car since they are not encumbered by seat belts. Just as one type of gun, or one style of holster may not be perfect for all occasions, one carry location may not suit all needs either.
Why carry a third gun? In addition to offering access options in multiple scenarios, having three guns allows me to give one to someone else (who is mistakenly, not carrying) in an emergency and still have a backup.
My choice of equipment, techniques and tactics are based on training and experience — others, and my own — all chosen for specific, well-thought-out reasons. Carrying multiple guns is not paranoid, it's simply being well prepared.