Student versus Master
Just because one can pull a trigger does not mean one knows how to use a gun. Can they handle being shot? Can they deal with shooting the wrong person? Can they deal with accidental misfires? They they deal with the gun jamming or malfunctioning? Can they handle having the gun being pointed back at them? All of these skills go hand in hand with knowing how to use a gun. Just because one can pull a trigger does not mean they can use a gun.
There are many skills such of this that cannot be taught in a school, in a book, by copying someone else, or thru repetitive training. Some skills can only be gained during real life or death experiences. The observer's effect. The act of observation affects the outcome of the experiment.