I had some insights while playing tennis today, applicable to most sports, and even some physical skills like playing musical instruments. What is a beginner: A beginner needs to simultaneously manage different modules such as eyes, shoulders, hands, hips, and legs, but only has one main agent to focus on. Focusing on A means forgetting B, resulting in neglecting one aspect for another. What is proficiency: Because some modules have developed muscle memory reflexes, sub-agents can be generated to process them in parallel in the background, no longer consuming the main agent's attention. The main agent can then handle higher-level coordination and decision-making. How a coach does it: Knowing how to strategically allocate the beginner's single main agent to the learner's different modules in a certain order, transforming it into modules that sub-agents can run in parallel. Following this model, when learning a new sport, consciously distinguishing the current priority of different modules, and to what extent the main agent is reducing the perceived presence of certain modules, should significantly increase learning efficiency.

Coincidentally, I just wrote about badminton yesterday, and I've been practicing my starting steps in badminton lately, which are somewhat similar to the shuffle step in tennis.