There are several reasons for being inconsistent, including your aiming technique. However, an even more important reason people can be inconsistent is if they are unaware of what their body is doing during the shot. One reason blank bale practice is valuable is because it can (if you let it) remove all the noise from your mind and let you focus on what your body is doing during the shot. You can learn perfect form from the best instructor/coach in the world, but if you are unaware that you put a little torque on the string from time to time, don't always relax your string hand, move your anchor slightly, or move your head during the shot, or 101 other things, then you will continue to be inconsistent. Becoming aware of what you are doing during the shot is a lifelong process. Once you learn to recognize the basic things, like those I mentioned, you will be a pretty good shot. Then you will begin to become aware of the subtle things that will make you an excellent shot.