Please read the post that I just put on the other thread on this subject regarding the Montana grizzly bear attack. This fellow was an experienced outdoorsman, and was apparently going fishing when he was attacked by that bear - presumably, he was going fly fishing there.
I‘ve fished that same area many times in the past, and there are thick, low bushes very close to the river’s edge all along that area. It would be very easy for a bear to be a few feet away and you’d never see it until it was on top of you. I wouldn’t blame the bear spray. It’s likely that the guy never have a chance to use it.
This subject has always interested me. It might have to do with the two separate, "Up close and Personal", incidents with bears that I had as a kid. I recently listened to a two-part podcast episode on "Ursinology" from the excellent, 'Ologies' series. The second part was a question and answer session provided by several biologists and conservationists who specialize in bears. The question on the effectiveness of bear spray came up and the answer was "YES", bear spray works. The biologist who answered said he always carries bear spray when conducting research and a firearm as backup. It was also mentioned that in order to be effective, you need to spray while the bear is still at a distance, not when it's charging you. Bear's hate bear spray and will leave at the scent of it. But bears can cover a lot of ground, very quickly and if you don't give them time to pick up the scent, it will be too late. This corroborates another online discussion where someone had taken time to list the firearms and cartridges used in bear attacks of people who survived. It was a long list that suggested that if it isn't a .44 mag or 12 gauge slug, 30-06, etc., you aren't going to make it. With that said, there was the one guy in Alaska who sucessfully defended himself with a 9mm pistol. Too bad he shot his own foot in the process. The funny thing was that at the bottom of the list, he showed that the most effective defense at 98% was bear spray.