There is no such thing as a fail proof mechanical devise! No matter how carefully it was produced, inspected and assembled, parts are sometimes flawed in a manner we can not see or know about until they fail. This is not just with guns but with every mechanical devise ever manufactured.
Yes, I would agree that revolvers were and still might hold the slight reliability edge against semi autos, but there is no denying the gap has narrowed. Narrowed enough now that I no longer EDC a revolver. The advantages to a good quality semi auto so far outweighs carrying a revolver, I have retired my 5 and 6 shooters for EDC.
I have stated here before that I have had several S&W revolvers fail to function and had broken. Broken Trigger and Hammer Studs, Hammer Noses, Springs, Sears, etc do occur.
Again, back in the day, yes revolvers were generally 5 or 6 "for sure" as they said, mostly, but not always true! Today's SA's have just about caught up! While SA's have gotten so much better, revolver technology has not changed much.
While back in the day manual transmissions were so much more reliable than automatic transmissions, that is no longer really true. Considering the numbers in which they are made, automatic tyranny's are now quite reliable!
While SA drills and clear jams are prudent & essential, if a revolver breaks, the only immediate use for it is as a set of brass knuckles. Hopefully everyone here has thoroughly tested and vetted their carry loads and know they are reliable and accurate.