Decompose Any Complex Skill into a Learning Tree

A big skill feels like a wall until someone shows you where the footholds are. Name the skill and this breaks it into a learning tree across three layers, foundation, core and mastery, with each node described so you can see the prerequisites, the baseline competencies, and what actually separates good from excellent.

Break down the skill of {SKILL} into a structured learning tree I can use as a roadmap.

Organise the decomposition into three levels:
- Foundation layer: prerequisite knowledge and micro-skills that must be solid first
- Core layer: the primary competencies that define baseline proficiency
- Mastery layer: advanced capabilities that separate good from excellent practitioners

For each node in the tree, give me:
- A plain-language description of what that sub-skill involves
- A simple self-test I can use to know when I've genuinely acquired it
- Its dependencies (which nodes must come before it)

Finally, highlight the single highest-leverage node: the one that unlocks the most other nodes if I focus on it first.