When I was 12, I was at a friend of my parents who had an older son. He was friendly to me and one time offered to teach me how to box.
He showed me how to move, block, and wait for opportunities to punch. It was all done in the kind of playful jousting, but with an undertone of mentoring.
All of a sudden I saw an opening and threw a right. It was going straight into his jaw when he caught my arm and stopped me. He was cordial and calm and took it in stride. I realized that I would have hit him hard if he didn't catch me.
Somehow I saw how he was just teaching, while I, not trying to hurt him, was playing more seriously. His restraint and focused calm taught me much about being within yourself to the point where you are not caught up in the activity you are engaging in.