You are having a lesson
Your issue is that your outside shoulder drops and turns to the outside on the right rein. Your coach explains what is happening and demonstrates how your body position is affecting your horse. You are very clear in your mind what is going wrong and what you need to do to rectify it. It’s your turn to show what you have learnt. You put yourself into position and off you go onto the right rein. You start off with the shoulders in alignment with the horse but before you have turned half a circle the shoulder has dropped and is tuned in the wrong way, exactly as you had before the instruction. You do it wrong.
Are you not trying? Are you a fool? Of course not, you are perfectly normal and have reacted exactly just as 85% of riders do. Why? Because of muscle memory. Most of us have come across this term at some point in our training, but it is not a memory stored in the muscles, of course, but memories stored in your brain. If you’re practising your riding skills over and over again, the idea is that you’ll continue to improve, after all ‘practice makes perfect’ right?