This is a great explanation! The biggest leap forward I made in my riding ability came with riding my instructor's school master for about 6 months - but only after 10 years of learning on green horses and horses in re-training (and one tricky-but-reliable school pony). Any earlier than that, and I'm sure I wouldn't have had the skills (she demands perfection from the rider) or the ability to appreciate and learn from the feeling of correct movements.