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What I Wish I Knew Before System Design Interviews

How to avoid common mistakes, crack the interview, and land a job at a big tech company

7 min readMar 24, 2025

Can you build a large, complex system like WhatsApp or Instagram within an hour? Yes, you can, but not in the real world — only in system design interviews.

You can read the free version of the article here.

In the real world, it would take more than a year or two to build a system at WhatsApp or Instagram’s scale. However, in system design interviews, you are expected to complete the design within an hour.

The ambiguous nature of the problems often overwhelms candidates. I have seen candidates get nervous and utter — “Is 1 hour sufficient to complete the design ?”.

System design meme

It’s important to realise that the goal of system design interview is not to design the whole real-world system. Its purpose is to convey your structured thinking, technical depth and breadth, and reasoning skills to the interviewer.

After conducting more than 200 interviews, I have realised some common mistakes that hold back a candidate during the interviews. But with thorough practice and hard work, you can work on them and successfully crack any design interview.

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Animesh Gaitonde
Animesh Gaitonde

Written by Animesh Gaitonde

SDE-3/Tech Lead @ Amazon| ex-Airbnb | ex-Microsoft. Writes about Distributed Systems, Programming Languages & Tech Interviews

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