Scaling modern applications from zero to millions of users demands forethought, not just more servers. System design is the architectural discipline of crafting resilient, performant, and maintainable distributed systems. It’s about making critical upfront decisions on data stores, communication protocols, and service decomposition that prevent catastrophic failures and allow for agile evolution. Learning system design now means mastering the blueprints of the internet’s most robust infrastructure and anticipating the bottlenecks before they cripple an application.