Hyrum's Law
Origin
Hyrum Wright at Google discovered this while migrating massive codebases. Even undocumented behavior — just "this is how it currently works" — becomes a dependency. Change validation order, polish an error message string, and somebody's code breaks. xkcd #1172 "Workflow" captures the same message: no change is safe.
Meaning
Stable API operation is harder than the spec — every undocumented behavior also becomes a spec. Why Linux kernel never breaks user-space compatibility in 35 years. Why Go enforces the "Go 1 promise". Hyrum captured the deepest truth of interface design.
Lesson — Meeting Eastern Classics
Zhuangzi: 庖丁解牛 — the butcher cuts oxen for 19 years and his blade never dulls. The secret: follow nature's grain. Hyrum's Law is the API's grain — ignore it (the grain finer than the spec) and every blade dulls.
"着" combines sheep (羊) with eye (目) — to fix one's gaze, to attach, to depend. Users attach to what we never intended. Analects: "A gentleman does not contend; if he must, like archery." One who is aware of 着 designs without contention.
