I want to meet the person who said they saw a person overpower bear spray as well as the person who "fought through it".
WHY? you ask? so I can lock them in a room with a big glass window and deploy a can and watch from a safe sealed location. Then eat popcorn and take notes, you know for sciences sake.
A few years ago I exploded a can in my apartment in mid January, it was a total freak accident.
Even with both doors open you couldn't walk in the door and make it 3ft. I left both door wide open for over an hour and went to go get PPE and cleaning supplies from work.
Went back in with goggles and a respirator and even still could tell the air "wasn't good". Place wasn't inhabitable for 3 days AFTER I went in and cleaned it up. Could still tell it was in the air a little bit 5-7 days after it happened.
My girlfriend was PISSED. Just one more thing to add to the load of straws on the camels back leading to me being single again

Personally I found it rather comical a couple weeks later, and really laugh about it now. So when people question how well it works I shudder and giggle a little. Maybe bears can overpower it but I question a human...
Morale of the story if you value your health and relationship. Don't deploy a can of bear spray in a confined space...