Epictetus points out that every skill or discipline has its proper domain and objectives - medicine focuses on health, architecture on buildings, philosophy on living well. This insight calls us to understand the specific purpose and methods of whatever we're trying to master, rather than expecting one approach to solve all problems or one skill to apply everywhere. It also suggests that becoming excellent at anything requires focused attention on that thing's particular demands and principles. Mastery comes from depth, not breadth - from understanding what something is for and how it works, then dedicating ourselves to that specific excellence.