There two additional problems with new shooters and old shooters which have a great impact on shooting.
Breathing. They don't breath or breath while they are trying to shoot.
Foot work. If the feet are not positioned properly then they will not be able to shoot accurately. This is really shows up in timed and rapid sequences.
A simple test is to align up on the target and then move the left foot right or left front or back. The alignment of the weapon in relation to the target will change dramatically.