If you are holding the firearm in your hand, and your attacker is less than about 20 feet away from you, they can easily get the jump on you.
This is the point that gun defense folks don’t understand and needs to be enforced: distance is ephemeral, a luxury, and time is usually against the defender in a stand off.
But these same folks are also the same crowd that says they can win in a fight with a bear. They have no concept of reality.