Rather a boring requirement. It is easy to get distracted from this by better…sights, trigger, rate of fire, grips etc.
People rarely say when buying a gun “I want the gun to always go bang when I load it and pull the trigger”. It’s a good thing that they don’t because that gun doesn’t exist.
When a gun does start to malfunction many people go into denial. It can’t be unreliable because the design is over 100 years old! It’s a revolver. It’s a glock. I shot thousands of rounds without a problem.
Problems happen. As an engineer there are many factors that affect reliability.
You might think that reliability is something that is important mostly for defensive shooters. It is a universal quality that everyone wants in their gun even if they are unaware they want it.
Competition is an obvious place where the shooter wants a reliable gun that shoots tens of thousands of rounds. However, the gun owner that rarely shoots is probably presents the most stringent demand on reliability. How many years do people own guns, rarely shoot them and somehow it can shoot when the finally do go shooting?