Large-Codebase Reasoning
Synthesis
A large codebase cannot always be held in one accurate, complete mental model. Sean Goedecke argues that partial understanding can be a rational operating condition when systems carry years of user-specific behavior, dependencies, compliance constraints, and turnover. His claim is normative rather than universal: rebuilding an abandoned system may discard important edge cases faster than careful revival can recover them. [src]
The useful unit of understanding is often a bounded flow: trace one behavior end-to-end, make an accountable change, observe the result, and enlarge the model only where the next decision requires it. In this view, an engineer should label uncertainty rather than confuse a locally useful theory with complete knowledge. [src]
LLM assistance changes the trade-off but does not remove it. It can accelerate formation of partial theories, while still requiring tests, observable feedback, and someone who owns the decision. That makes local reasoning and verification complementary rather than competing practices. [src]
Practical implication
For an unfamiliar system, prefer a reversible, instrumented path over premature architectural certainty: name the specific flow, state the assumption, run a check, and record what changed the model. Escalate from local reasoning to broader design work when cross-cutting invariants, security boundaries, or repeated failures demand it.