--- name: rule-of-three description: Structure complexity into about three memorable chunks with a rhythm - the phone-number principle - for systems, workflows, names, and output. --- # Rule of Three ## Use This Skill When Designing or naming a system, workflow, API, or process; deciding how many sections, steps, phases, or options to present; or organizing output that is getting hard to hold. ## The phone number A US phone number is ten digits, but nobody remembers ten digits — they remember three chunks: area code, prefix, line number. `(931) 381-XXXX`. Two things make it stick: 1. **Chunking.** Ten digits broken into three sections is far easier to memorize than ten in a row. Grouping reduces cognitive load — the same reason card numbers and IDs are spaced, not run together. 2. **Rhythm.** Three chunks give it a cadence you can say aloud — one-two-three. That beat is why three-part phrases land and repeat: _Veni, vidi, vici_; _stop, drop, and roll_; _Post. Build. Ship._ Structure things the same way: take complexity, chunk it into about three sections, and make the three say with a rhythm. ## Why it works Three is the sweet spot — enough to be complete (beginning / middle / end; propose / act / verify), few enough to stay memorable, hold a beat, and let you do each part well. ## Apply - Group a flat list of many items into ~three sections — ten digits into three chunks. - Give a system three top-level parts and name them as verbs or roles you can say in one breath. - When something feels sprawling, ask "what are the three?" before adding more structure. ## Resist the fourth A fourth top-level chunk usually means the model is wrong — fold it into one of the three, or rethink the decomposition. It also breaks the rhythm. Equally, do not force three where it is artificial; three is a strong default, not a law. ## Evidence in this codebase Post.Bid.Ship. Post.Build.Ship. architect / developer / gatekeeper. frontier / workhorse / light. workflow / guidance / reference. Threes — because they are easy to hold, easy to say, and easy to do well.