I'm not sure why the bear would present any problem to a downhill skier simply because you can continue on your path much more rapidly than that lumbering bear. But let's say that you were doing cross-country skiing and that bear seemed more than able to charge into your path.
It is the plasticity of the affect system that allows you to shift from one source of affect to another; remember the image I've offered of the affect system as a bank of spotlights going on and off in response to the triggers for each. The onrush of thoughts associated with the known danger of bears moves consciousness and attention toward bear stuff and away from gosh I'm skiing. That is the function of the affect system---to allow you to use the best part of your neocortical apparatus under conscious control when affect brings some source into the spotlight.
Only when we are enjoying or interested in a particular source of positive affect, and something interferes with our ability to remain focused on that source even though the original source remains a competent trigger for either positive affect, only in that situation does the impediment to positive affect trigger shame affect. You and your beloved are smiling at each other when all of a sudden an errant thought crosses his/her mind. Immediately the face of your beloved changes to reveal not the relaxed smile of contentment but whatever affect fits best this new thought. You are still interested in or capable of enjoying that other person, and quite willing/able to continue communing. But for the moment, the other's face is an impediment to the continuation of your pleasure. Shame affect is recruited as an amplifier of this impediment; it turns you away from the now-problematic scene, etc. etc. etc.
In terms of the spotlight image, I have suggested that the spotlight for shame affect is a "darkness beam" that obscures whatever it is aimed at. (A firm background in science fiction helps when you decide to become a theorist of any sort!) It is unlike the other beams in that it does not actually illuminate but obscures much as shame turns us away from whatever a moment ago had seemed so interesting or enjoyable as it was illuminated by the beams for those affects.
By the way, Rich---I don't know where you live, but you might consider joining the Tomkins Institute and working with one of our study groups. You seem to have gotten the idea of affect theory quite well and might like to delve further into this work. Any other readers of BOL are welcome to join us as well.