When you move beyond junior roles, companies don't just want someone who can write functions. They want someone who can design systems that don't break when real users show up.
Scalability isn't an accident. Your code may work for 100 users — system design makes it work for far more.
Caching, load balancing, queues, and distributed thinking aren't interview trivia. They're production survival tools.
Good design reduces firefighting. A well-designed system means fewer outages, fewer bottlenecks, and more sleep for the team.
If you want to grow into senior roles, start learning how systems actually run at scale.