When I ask for students to expound upon this question, it usually comes down to a question about which handgun is reliable. My answer to this is not a popular one. It's not the answer that anybody wants to hear. But it is a fact of life. The answer to this is that no gun is completely reliable.
To be sure, there are a handful of gun models out there that have a very poor reputation when it comes to reliability. But even with guns that have a solid reliability rating, they are mechanical devices. What happens to all mechanical devices at some point? They fail!
I have had some students proclaim that they carry a revolver so they don't have to worry about this. Well I've got news for you, revolvers are capable of failure too. I have seen more than my share of revolvers on the firing line that end up having the cylinder bind on them. I have also seen a couple where the firing pin failed to properly strike the cartridge, causing failure.
You may argue that planning to fail is a negative mindset. I will vehemently disagree with you. Failure is a realistic possibility; we can choose to ignore it, or we can choose to accept and train for it. Winston Churchill once said, "He who fails to plan, is planning to fail." So I contend that you are planning to fail one way or another. Either you plan for failure proactively, or you let failure plan for you.
A good firearms training routine will regularly include both Primary Malfunction Clearance drills and Secondary Malfunction Clearance drills. It is important to practice these until they become second-nature. If you do not make these a routine part of your training, you will find yourself in a world of confusion when a malfunction occurs.
Go to any range on any given day. I virtually guarantee you will see somebody experience at least one malfunction. If they have not trained for this, you will see them do the same thing. Stop, look at their firearm (often pointing it in an unsafe location), and try to evaluate what the problem is.
By implementing the Primary Malfunction Clearance, you will clear approximately 90% of your malfunctions. You will do this without ever taking your eyes off of your target (or threat). If that does not work, you should immediately move to the Secondary Malfunction Clearance. This will clear most other malfunctions. Again, you can do this without ever taking your eyes off target. If these two do not clear your malfunction, you officially have a "jam". This is not something that you can clear by yourself, it will require a gunsmith and tools.
Practice these techniques and prepare yourself for success.... by planning to fail!