Szymon's core methodology: when a legacy system encodes critical business rules that no single person understands and documentation is sparse, stop trying to discover rules through static analysis or full test coverage. Instead treat the running system's behavior as the specification: record inputs, outputs and side-effectful interactions in production, rebuild the new flow, replay the recorded interactions as stubs, and assert identical outcomes. This gave the Lemonade rewrite confidence without extensive up-front unit tests.