Lee Enfield at War

[Seaspriter]

using an eye disc
As a Yank who was trained in the military and earned a service ribbons for marksmanship, please help me understand this "ordeal" with the eyepiece. When I first saw the pic I was puzzled and confused. The first two things we were taught in Navy/Marine training was NEVER to point a gun at another human unless you intended to kill someone, and to check the magazine & chamber to be sure both were empty.

The training of a marksman started in the mind. Pointing the gun at a drill instructor was just totally the "wrong mindset." I never saw anyone point a gun at a drill sergeant or gunny instructor. If I even thought of such a thing, latrine duty for a year would have been mild punishment; running a bayonet up my butt might be a more realistic punishment -- it was a typical drill sergeant's threat. What was the intent of this seemingly bizarre training exercise?? What am I missing?