That only happens when hunters are hunting the bear, not when the bear is hunting the hunter. Bears sneak up on you or charge out of dense brush. Short Faced bears would eat a large Grisly for breakfast - you would be a snack on the way to dinner.
No one said "fire arms are not effective against bears" - just that only works when you have a fire arm, and are aware of the nearby bear. Else its becomes a different story ...
Be sure you have a large enough caliber ...