Odd situations do happen. There was the citizen who defended the police officer in the trailer park with a 100+yd revolver shot recently. The high-profile example would be the Fairchild AFB shooting in 1994, where an AF SP killed the shooter with a 70+ yard head shot with his M9.
The happen far more often than people realize. That is why your training should include marksmanship skills as well as bad breath distance. You should not just train for "My Gunfight", it probably will not be anything like what you envisioned.