How about that once in a while a cannon or archer tower will miss a shot or two. It won't happen every other shot, but the archer tower will miss a shot once every 50 shots or something. It makes the game more realistic because you cant hit your target every single time. At lv 1 it occurs more often because of less "training" and at lv 13, it happens less often as it had more "training". It won't happen often, but it will happen like 1/50 for lv 13 archer tower and 1/20 shots for lv 1 archer tower.