When a semi-auto pistol has been properly lubed, has a perfectly working magazine with no glitches, and has well made ammo that hits a minimal level of power generation, and the gun is gripped firmly, it will run all day long and in the worst conditions. However, when just one of those things is off, it can bring down the entire functionality of the pistol. 

One of the biggest issues is that of the ammo. If the ammo cannot power the slide, the gun will not work, regardless of any action by the shooter. In some guns in certain situations, a ton of time and effort go into figuring out what ammo will work in a particular pistol. The venerable 1911 is famed for being persnickety with specific types of ammo, and much work can go into figuring out what combination of springs, ammo, and grip will make the gun reliable. Even the Glock in all of its “perfection” has issues at times. The Gen3 .40 caliber guns were notorious, as were the first iterations of the Gen4 models (even in 9mm) in having problems, and a lot of people have found that putting a PMO (pistol mounted optic) on one can make the gun go wonky until the right springs are installed. 

Another huge factor can be shooting in odd and compromised positions such as lying sideways, compressed in with someone on top of you, or weak handed shooting when you are not standing perfectly upright. I cannot begin to coin how many times I have seen perfectly reliable pistols go cockeyed in shooting classes when these elements get introduced. If there is any lessening of the support behind the frame of the pistol while the slide reciprocates, bad things can happen. 

None of this has EVER applied to any double action revolver produced since WW1. As long as you can pull the trigger, the gun will run. You can be in the most compromised position possible, with a weak grip and l;ittle support behind the gun, and firing the weakest ammo possible, but if you can work the trigger, the gun will go bang. That is a tremendous plus to a wheelgun that cannot be matched by any semi-auto pistol ever made. Bar none. 

Where this is particularly useful is when a shooter has physical issues. As an example, let’s look at a gun I ran for over six years on almost a daily basis, a Ruger LCR in .327 magnum. In .327, a Speer Gold Dot gives really nice results with expansion and penetration. It is also accompanied by flash bang level noise and flash, and hand shaking recoil. In a snub, it is not fun and I believe it leads to lessened shooting performance, so I do not carry that ammo in my LCR. Generally I run .32 H&R Magnum ammo. Still exceptionally good results ballistically speaking, but a bit more manageable shooting wise. And going down in power has zero effect on the functional reliability of the gun. 

Even better, for those who have hand strength issues (such as arthritis), you can go down even more to .32 Long. With the right loading such as XXXXXXX 100 grain wadcutter, you have a super accurate round that will absolutely give you the needed penetration, but feels like shooting .22 LR rounds. So even a weaker person can have a load that will give them a solid chance of stopping a bad guy without making it impossible to shoot, and possibly even encourage someone to practice more because it is fun to fire. 

None of that is possible with any semi-auto pistol. Putting a lightly loaded round into a Glock is a good recipe for failure, but with a revolver it is non-issue. 

Along the same lines, if the good guy defender finds themself in a compressed or compromised position, with a poor grip, the wheelgun will still have the ability to empty the cylinder into the bad guy as long as the shooter can work their finger. 

Again, try that with any semi-auto and it is literally a crapshoot whether the gun goes off or not. 

And god help you if it does fire once, but then the slide catches on the slightest bit of resistance from cloth or body parts. You have the very definition of a failure to feed. 

A lot of people who have taken classes in entangled fighting where Simunition guns are used will bemoan how unreliable those guns are. The truth is they are extremely reliable if you are firing them at arm’s length with a good grip and nothing interfering with the slide. I have never even seen a failure to feed in that situation. The reason they fail in those classes is that none of the above conditions can be met during the actual training evolutions. As soon as less than ideal conditions are introduced, formerly ruggedly reliable guns become jam-o-matics. It is why those of us who teach that material have a specific retention shooting position to minimize the interference as best as possible. With revolvers, those things are less damaging to the shooting cycle of the wheelgun. 

To sum up, one of the strongest positives to using a revolver fro self-preservation is that you have far more flexibility in ammo choices, and you have far more flexibility in knowing that the gun will cycle in rough conditions.