I was first introduced to the "wheel of misfortune" during my departments firearm instructor school. The term comes from the Army Marksmanship Unit. I was in the Army and have a certain amount of pride associated with that, so it was really funny to hear a former Marine admit the Army had come up with a fantastic marksmanship training tool.
This particular diagram comes from Glockparts.com but is essentially the same as the one from the AMU. My favorite part is that it applies to all pistols, not just Glock's. If you are having a marksmanship issue, take a look at this diagram and you can likely diagnose what is going on. Even working with extremely skilled instructors, they can only tell you how to do things the proper way. The most important element is what the shooter is actually seeing/doing, and an instructor doesn't have a way to look through your eyes.
It's so common to ask an inexperienced shooter a question, and they give you the exact answer they want you to hear, even if that's not what's really happening. By taking a look at this, experienced shooters can help themselves, and inexperienced shooters can let the instructor know what's happening simply by grouping on a target. Why didn't I think of this?