In the dynamic landscape of modern software engineering, balancing rapid feature delivery with sustainable architectural integrity remains a perennial challenge. This paper examines the “You Aren’t Gonna Need It” (YAGNI) principle—originating from Extreme Programming—as a disciplined antidote to speculative overengineering. We trace YAGNI’s theoretical foundations and explore its core tenets: implementing only immediately needed functionality, embracing change through iterative development, continuous refactoring, and validating design decisions with real user feedback. Through a detailed microservices case study—illustrating the evolution from a simple monolith to targeted service extraction and just-in-time data pipelines—we demonstrate how YAGNI-driven decisions mitigate technical debt, streamline feedback loops, and optimize resource allocation. We then address common obstacles, including stakeholder pressure for “future-proof” features, compliance constraints in regulated domains, and the risk of under-building fundamental system qualities. For each challenge, we propose practical strategies: rigorous backlog grooming, decision-logging, automated testing, and cross-functional collaboration. Finally, we outline a set of best practices—such as feature flags, refactoring sprints, and agile metrics—to foster a culture of measured simplicity. By applying YAGNI in concert with Lean and DevOps methodologies, engineering teams can achieve architectures that grow organically with validated demand, yielding robust, maintainable systems that maximize immediate business value without sacrificing adaptability. In this talk, you will understand how to deal with "trade offs" between over engineering v/s extensibility. Its very hard to strike this balance, and judgement calls/mistakes in such tradeoffs can usually be very expensive - to the tune of millions/billions of dollars! Listen in with practical examples, the why's/why not's and the spirit of YAGNI!