Watch videos of electric fences and you see the same response...until you don't. There's a great video of a black bear shimmying under an electric fence: https://www.youtube.com/watch?v=_gMC11x1luA

The nice thing about appropriate firepower is that it is fatal to the bear. The guessing is over, the equation has ended, and you can collect your thoughts and asses things in peace without wondering how much is left in your can. If you are very lucky you get to wonder whether the bear will come back for another go.

If "success" means a bear hit full in the face from 20 feet away with half or more of the can used and the bear not only getting you but starting into you with claw and fang... Might I kindly suggest redefining success? Now you are out at least half, the bear (who it has been proven likes and is attracted to the spray) is still around and you get to wonder and wait and repair... Success you say?