A metaphor for stages of technical build maturity, borrowed from a well-known IT-strategy model and used by Barham to argue against both overengineering and underengineering: pioneers explore rough, unvalidated territory and should build cheaply and fast; settlers turn a validated idea into something repeatable and maintainable; town planners industrialize the mature, high-scale parts of the system. The argument cuts both ways — don't build town-planner-grade architecture under a pioneer's unvalidated desirability/viability, but also don't leave a settler- or town-planner-stage system running on pioneer-era shortcuts once the problems it causes are known. See "Don't Scale Expensive Problems" (Architectural Debt Mistake) for what happens when that second failure mode is ignored.