For me it was anxiety over the sight picture and stressing over the anchor. I worked on drills to get comfortable at anchor. To be fair it was many drills, lot's of close bail work. And most of all it was back to square one. Most of us just grab the bow and go for it. How much time do you spend working on your string grip, bow arm, bow grip, can you identify precisely your anchor, how in touch are you with your form. Do you use your back muscles. The big one for me was learning to be at full draw and having both arms in a more relaxed state, ie held the bow with solid back function. Form there it was working on a true dynamic release and for me that does not mean touching the shoulder after the shot, that is too exaggerated for me. So to answer the question is the trick is true dedication, not just shooting but educated shooting.