You just landed an on-site interview at your dream company. The schedule lands in your inbox. Most sessions look manageable — coding, behavioural, a hiring manager chat. Then you see it: System Design Interview.

Your stomach drops.

“Design Twitter.”
“Build a URL shortener.”
“How would you architect YouTube?”

These questions feel impossibly broad. How could anyone design a system that took hundreds of engineers years to build — in 45 minutes? Here’s the secret that most engineers miss: