In defense of not understanding your codebase

The author challenges the traditional software engineering philosophy—often associated with Peter Naur’s "Programming as Theory Building"—that a codebase must be fully understood by developers to be effectively maintained. While this approach works for small, stable projects, the author argues it is impractical for large-scale corporate systems where complete understanding is impossible due to the sheer volume of code, legacy quirks, and team turnover. Instead, engineers must embrace a "partial understanding" model, where they learn the system incrementally by isolating specific flows and making educated, confident changes.

Ultimately, the article frames "maintaining a mental theory of the codebase" as one engineering value among many, often to be weighed against business needs like speed, legal compliance, or project scope. While a total mental model is ideal for personal projects, professional software engineering requires a more pragmatic, "impure" approach. In large, complex environments, the ability to work effectively without total clarity is not a sign of failure, but a necessary skill for navigating the reality of modern software development.