I think this topic is funny. What makes something 100% reliable? Everyone may have a different answer. What are the characteristics that meet the criteria? If you get FTF's because of a weak mag spring, is the gun not 100% reliable? If you never clean it and it jams, is the gun unreliable? If you bring a gun out of the safe once a year and run 100 rounds through it without incident, does that make it reliable or is the sample size too low to be considered 100% reliable? What about bad ammo? Even factory ammo has a percentage that is out of spec. If bad ammo jams it, does that make the gun unreliable? If it fires on out of spec ammo, does that mean the chamber is oversize?
As others have said, parts are going to break because it's a machine - even with the best of preventative maintenance. I've seen O/U shotguns, a relatively simple gun, not fire (and double fire) simply because it needed to be cleaned.