The idea of a novice dealing with a dangerous bear situation is somewhat disconcerting, particularly if that individual has never killed a large animal. First off, if they're full grown and have never killed a large animal they might not have the personality to prevail. They certainly haven't had the interest or opportunity to experience that, and without some practical experience, a dangerous game scenario is a tough way to get blooded. They might have an unrealistic expectation of what their gun can do or of what they can do with it, or they might not be able to bring themselves to shoot when they need to. They might be concerned about legal ramifications of shooting, they might be thinking that what is playing out before their eyes can't be real. In any case, they are in an mindset that will not allow them to save themselves or anyone else.
I heard about such a situation recently where an unarmed young guy who was examining a dead beluga calf, was charged by a bear which took exception to his presence. His partner who was a short distance away in a boat didn't shoot, despite having a loaded gun, being in no peril himself, having a good target angle, and a large target. When the young guy realized he had nothing to loose, and couldn't outrun the bear, he turned and ran straight at it, causing the bear to turn away. That gutsy move undoubtedly saved his life.