Software survives when the team holds a shared mental model of its code; churn breaks that theory, causing bitrot and project death.
Software longevity depends on a team's shared mental model of the code, which the article calls a "theory". When the original programmers leave, that theory dies and the program can no longer be reliably modified, even if the binary still runs.
A programmer who was there when a module was first written has the most accurate theory of how it fits together. Those "first-generation" developers can answer change requests intelligently. Second-generation developers inherit the theory by working alongside first-generators, but over time the proportion of first-generation knowledge erodes if churn is high.
The piece links churn directly to bitrot: not only do dependencies change, but the mental models of the people maintaining the code fade. When a developer's internal theory diverges from reality, they either rewrite code unnecessarily or cannot safely modify it, leading to wasted effort and hidden defects.
Leaders should prioritize team stability, mentor newer engineers to become first-generation thinkers, and create deliberate knowledge-transfer rituals. Rapid scaling without preserving the original theory creates a cycle of rewrite and slowdown, jeopardizing project outcomes.
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