All of us have been there. Yes, the biggest reason in my opinion is, not "focusing on the spot". Along with that overthinking the shot. If you practice all year round, and focus on the spot, your arrow will go there. I had a friend that struggled with this and I worked with him the whole year, the next season, she smoked three of them. To me, if I decide that I am going to shoot the animal, the rest of the world is tuned out, I focus on the spot, the next thing I know the "shot" just happened.