A legacy Java codebase presented challenges due to its plugin system, which lacked a formal API, causing developer uncertainty and fear of breaking changes with every update. Although the plugins allowed rapid shipping and problem-solving for customers, their reliance on undocumented features often resulted in unintended consequences when changes were made. The company eventually overcame these issues by implementing explicit testing for popular plugins, developing a formal API, and replacing the product with a more extensible version. The broader problem of developer uncertainty, which delays project timelines, can be mitigated by implementing strategies such as adding comprehensive tests, using type-safe languages, defining clear service boundaries, and minimizing the context-switching required by developers. The text emphasizes the importance of reducing the cognitive load on developers by creating templates, guardrails, and formal APIs, thereby enhancing confidence and speeding up the development process.