You, an armed citizen, are infinitely more likely to get into an entanglement and have an opportunity to use a knife than a soldier is. Soldiers usually have friends...lots of them....with lots of guns. We usually don't.
Everyone else already hit on the reasons to carry a knife. Keep in mind that pistols aren't death rays, and even filled with bullet holes your assailant could still tackle you and put on a hurtin' until he exsanguinates......and the chances of that are not a vanishingly small. Pistol employment can be complicated to impossible during an entanglement, and a knife makes sense. It's giving you another option, with little space or weight needed.
Finally, training is awesome. More training is always better. With that said, it doesn't take a whole lot of repetitive training to be dangerous with a knife when employed reverse grip, edge in (RGEI). I attended a FMA knife seminar that BaiHu hosted, and our class focused on reverse grip edge out. Being the curious one I am, I asked our instructor about RGEI. In summary, his response was, "that's some really sneaky, dirty stuff.....even by a FMA standard. When you see a person using RGEI, he either doesn't know what he's doing, or he really knows what he's doing. In either case, he's incredibly dangerous."
So, consider that along with the ammo shortage right now. It may not be feasible to shoot a lot right now......but you can still train on knives. And if for whatever reason you can't train on knives consistently, you're likely not to lose as much capability in its employment as you are with employing a pistol. RGEI is so intuitive (especially if you have any fighting background whatsoever), that IMO it is not as perishable a skill as pistol employment. Of course, this isn't an excuse to not train, but it is something to consider. Training in RGEI also gives you skills that transfer over to other weapons of opportunity....screw drivers, pens, ect.
Finally, you can usually take a knife more places than you can a gun.
"Are you ready? Okay. Let's roll."- Last words of Todd Beamer
All of that makes sense, though I'd not try for a knife if I were struggling for control of my firearm with someone. I have actually been stabbed in a fight. The man was trying to rob me and, being a bit drunk and unarmed (and 19) I told him something along the lines of what he could do with his knife. He slashed and jabbed at me, I don't know if he was seriously trying to cut me, and I tried to grab it and it went right through my hand. From the base of the palm straight up to the pinkie finger. Through and through. I still have no sensation on the flat of my right hand from the nerve being severed. Luckily for me, he ran once he saw he'd cut me. It was one of the major factors for me to get my permit at age 21. He could have killed my stupid, immature silly ass. I think situational awareness is probably THE most essential thing for safety. In the above incident, I was leaving a university bar (GO TIGERS!) catering to the grungy/hippy/nonfrat-sorority type of kids and cutting through a dark lot to my car. Drunk and paying no attention. If you know Baton Rouge it was Chimes street, about 4 blocks from what locals call 'The Bottoms,' a ghetto just outside the south gates of LSU with a murder a week. ZERO sense or situational awareness. God watches over...you know the rest.
Back to carrying a knife, how is it possible to carry an effective fixed blade? I've got a knife my father made me (he makes knives as one of his hobbies - canoes/kayaks/pirogues and bows, too. can u tell i'm proud o him? 67yo!) and a Kabar and that's it for my fixed blades. What is recommended and more important how carried?
Nice!
And, just as a primer, know that some RGEI techniques feed off this tendency of people to block with their hands. When your assailant makes an attack at you with his knife, you instinctively throw up your hand/arm.....and instead of just getting a clean defensive wound from a jab, you now have your assailant clenching your appendage between his blade and wrist, while he drags it....making a terrible mess of your tissue, if not completely fileting your arm.
So, given your experiences, I'm sure you can see how much more effective a knife being used RGEI would have been than just pointing the sharp end at you...and ultimately, how viable a self-defense tool it becomes even with guns in the mix.
"Are you ready? Okay. Let's roll."- Last words of Todd Beamer
After Southnarcs ECQC I started filling the void that was my unarmed and contact weapons skill set.
Just lucky that my focus on non-firearm skills coincided with the ammo drought.
BJJ/MMA 3 nights a week, knife, sap and handgun dry fire practice at home 2 nights a week, 1 light range day a week (usually 50 rounds) and on the 7th day I rest and train my mind on the internet.
"For a moment he felt good about this. A moment or two later he felt bad about feeling good about it. Then he felt good about feeling bad about feeling good about it and, satisfied, drove on into the night."
-- Hitchhiker's Guide to the Galaxy --
I understand now why carrying a knife in addition to my 642 is a good idea. I appreciate the pic, too. Seems a good, discrete (and safe) way to carry it. Now I've gotta find a suitable knife.