Hey Reader,

Welcome back to Guided Growth where we talk about the skills that accelerate your career beyond just writing great code.

This is The Unwritten Rules #2: a 4-part series where I share the career rules that exist but nobody shared them with you.

Last quarter, I interviewed 11 candidates for a senior backend role. I asked all of them: "Design a URL shortener."

7 out of 11 gave me the same answer. Same structure. Same buzzwords. Same diagram that looked like it came from the same YouTube video.

"Read-heavy system. NoSQL database. Base62 encoding. Redis cache. Load balancer. Scale horizontally."

It's a correct answer. On paper.

But when I can predict what you'll say next, it tells me you borrowed this knowledge. You didn't build it.

One candidate, let's call him Rohan, started differently:

"Before I design anything, how many URLs per day are we expecting? And is this a public tool like Bitly or an internal tool for a marketing team?"

Two questions. That's all it took. Because the design for 1,000 URLs a day is completely different from 100 million. Most candidates skip this step and jump straight to drawing boxes.

It's like a kid who memorizes "7 × 8 = 56" but can't figure out how many chocolates to buy for 7 friends who each want 8.

Three things tell me you learned from videos, not from building:

You over-engineer from the start. Microservices for 500 users. Kafka for a system that doesn't need event streaming.

You can't answer "why." Why Redis and not Memcached? Why NoSQL and not Postgres? If you pause, I know you picked it from a template.

You never mention failure modes. Real systems break. Builders know this because they've seen it happen.

My advice: build the thing after you watch the video. That one weekend project teaches more than 10 tutorials. When I ask "why Redis?" you'll say "because I tried without it, and the latency was terrible."

That answer can't be faked.

Know someone preparing for system design interviews? Forward this to them.

That's The Unwritten Rules #2. Next Thursday: the non-coding question I ask every candidate and the answer that decides everything.

Thanks,

Abhishek

The Guided Growth