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iteration

Use this skill whenever the question is *how* to develop a design — through one big push or through repeated cycles of build, test, learn, refine. Trigger when planning a design process, scoping an MVP, deciding between waterfall and iterative delivery, planning research cadence, or reviewing why a project drifted from its original vision. Iteration is one of the foundational principles in 'Universal Principles of Design' (Lidwell, Holden, Butler 2003) — and one of the most-violated by teams that try to ship "perfect" first versions.

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# Iteration

Iteration is the practice of repeatedly cycling through design, build, test, and refine — using each cycle's output to inform the next. The core insight: design problems rarely yield to single passes of careful planning. They yield to cycles, where each pass uncovers issues invisible to the prior pass. The teams that internalize iteration consistently outperform those that try to plan the perfect solution up front.

## Definition (in our own words)

A design that emerges through iteration is built by repeating a small set of operations: design something; build a version of it; test it (with users, with data, with a critical eye); learn what worked and what didn't; refine; design the next version. Each cycle reveals problems that couldn't be predicted from the inside of the previous cycle. The total work to reach a good design through iteration is usually less than the work to reach the same quality through up-front planning, because iteration converges on what users actually need rather than what you predicted they would need.

## Origins and research lineage

- **Lidwell, Holden & Butler** (2003) distinguished two types of iteration: *design iteration* (the planned, expected refinement during the design phase) and *development iteration* (the unplanned, costly rework during build that indicates inadequate design). The first is good; the second is a failure of the first.
- **Henry Petroski**, *The Evolution of Useful Things* (Knopf, 1992) and *To Engineer Is Human* (St. Martin's, 1985). Petroski's central thesis: useful objects evolve through accumulated failure and refinement, not through a single brilliant design moment. Successful designs encode many cycles of iteration.
- **Eric Ries**, *The Lean Startup* (Crown Business, 2011). Translated iteration into product-management vocabulary: minimum viable product, build-measure-learn loop, validated learning. Influential across software product design.
- **Tom Kelley & David Kelley** at IDEO, *Creative Confidence* (Crown Business, 2013) and earlier IDEO publications. Codified design thinking as an iterative discovery process: empathize → define → ideate → prototype → test → repeat.