I've been with new hunters and some older ones that got excited when seeing deer. Many look right over the rear open sight and shoot right over the deer, even at 30 yards or so. One of my adult friends had never killed a deer, but shot at several with his Win. 94. One day, I had him bring his rifle to the project field office trailer and I brought a drill press, a Williams 5-Dollar receiver sight, and higher front sight. After taking him to the range and sighting-in the rifle, he made a nice group offhand at 50 yards.
The next time he went hunting, he saw a deer in the woods at about 40 yards and drilled it in the heart. It started running, so he shot again, killing it instantly with a BRAIN SHOT! He never had a problem killing things with that rifle again.
Another teen friend using his open-sighted Marlin saw a buck standing broadside at about 40 yards. He had only 5 rounds with him and I heard 5 shots about a hundred yards from me in the woods. I waited a minute, then yelled, "Did you get it?" He yelled back, "NO". I asked which way it went. He yelled back, "He's still here, looking at me." It then walked off and we never saw it again. We mounted a receiver sight on that rifle too.