I have found for myself that when I start grouping arrows to the right or left, and can't seem to find the bullseye, I automatically assume a poor release or poor grip. Pretty soon, I am spraying arrows all over the place.
What I usually figure out when I stop and concentrate on form, is that I am short drawing. When I use back tension, push my bow arm out, and do not collapse or hunch my bow shoulder, my groups immediately tighten and fall back on target. My bow seems to shoot quieter and my arrow flight improves. I would gues when I short draw, it is about 1 to 1.5 inches on average, but have not videotaped myself lately. I bet that when I do, though, I am much more conscious of form.
I have also noticed, along with others on this post, that many trad shooters tend to short draw, even when shooting 45- to 50-pound bows. Some shooters are certainly overbowed, but I don't believe that is always the cause of short drawing.
Great post Mike!