Here you have an
of how polite they are.
Last year we accidentally ran into a grizzly mom with two cubs pretty close - mom was very cool, the problem in this case was that the cubs are hopefully not too curious coming towards you. All I can say is that it happens pretty quickly (we still don't know how she could appear so suddenly), but they also move on pretty quickly. You must have really bad luck to get into serious trouble. Retreating on a narrow trail keeping an eye on the bear is very theoretical - I have the impression that they know that they are better in the field looking at this stiff hikers.
. Overall: don't run, stay calm. And overall it's still not very likely to meet an overly interested bear. Make noise.