I agree, however some folks me included do not display a dominant eye. People are always saying "just make an opening between your palms and sight on a distant object...." well duh, I've only been shooting for forty years and I've tried left eye open, right eye open, both eyes open, left handed, right handed, etc. I shoot right handed, close left eye. It's hard for those who do have a dominant eye to grasp this, but if a person does not have a dominant eye that person must close one eye to aim. It does slow down target aquisition and affects depth perception but there is no other way, short of wearing a blinder which would be fine for shooting at stationary targets from a stationary position but is less practical for any type of dynamic shooting. For example, I recently took up IDPA. I have not shot a match yet, just holster training and a classifier. At holster training, I tried both eyes open. However when shooting around cover with both eyes open I see two cover edges, two guns, and two targets all about an inch apart. My eyes want to cross trying to pick which gun and target to pick.