As the scale of complex system software expands, we face unprecedented challenges. The dependencies among software libraries are becoming increasingly complex across platforms and languages, and a complicated build environment can directly affect both reliability and reproducibility. Meanwhile, other engineering challenges—ranging from tracing software vulnerabilities to orchestrating multiple CI pipeline tasks and using caching to cut down build effort and time—may seem unrelated on the surface, but they actually share one central cause. By focusing on this single cause, we can greatly improve reliability, efficiency, and cost-effectiveness in building large-scale software systems. In this talk, we will reveal the core idea linking these issues and present practical strategies to handle dependency complexity, improve build reliability, and balance development efficiency, stability, and cost-effectiveness. With this unified perspective, we can more effectively tackle the varied problems that arise in large-scale software systems.