3 reasons great developers still fail System Design Interviews
At Meta, I saw many talented candidates make these mistakes. Here’s how to avoid them.
In my 15+ years in tech, I’ve conducted hundreds of System Design Interviews (at Facebook, Microsoft, and now Educative).
I’ve also seen great engineers fail them.
If you’re not confident in System Design Interviews, you’re not alone. System Design Interviews are built different. With multiple valid solutions, the real test is your reasoning and communication.
Today I'll cover 3 common pitfalls I've seen in SDIs, and share the advice I wish I could've given to candidates who struggled in our interviews.
3 Common System Design Pitfalls (and How to Avoid Them)
1. Being too passive
At Facebook, I once interviewed an E5 candidate who froze, waiting for us to say more beyond the initial problem we gave him. Even with his experience, he became a no-hire.
Why? He was waiting for us to lead, instead of leading us.
When you're asked a vague problem, it’s your job to clarify scope, define requirements, and drive the conversation forward. Some interviewers won’t help much, and that's on purpose. That’s your chance to show composure and initiative.
You can take the lead by:
Walking the interviewers through your plan: “Once we’ve covered the high-level design, I’ll discuss monitoring and failure recovery.”
Asking strategic questions: “Which metric matters more for the business — latency or availability?”
Proactively evaluating your design: At the end, when you've finished your design, you can show your critical thinking by discussing other ways you might have approached the design.
Interviewers want to see hires who have the potential for long-term growth. Leading the conversation and navigating ambiguity is how you show leadership potential and product-level thinking. If you wait for permission or guidance, you lose.
2. Designing with your head down
I can't tell you how many candidates have presented solid designs and still fail. Why? They didn’t explain their process.
Your interviewers actually care more about your thought process than your final design. We want to see how you prioritize, make trade-offs, and iterate.
You should not be designing with your head down to the paper (or whiteboard, for that matter).
Here’s how to make that thinking visible:
Communicate constantly: Even 30 seconds of silence is too much.
Adapt quickly: If your interviewer adds a new requirement, show how you adjust your design.
Justify every choice: Explain why you’re choosing one database over another or why caching is essential for latency.
Most of us don’t naturally verbalize our thoughts while designing. That’s why practice is crucial to helping you get comfortable designing while explaining every step.
3. Getting lost in a tangent
Some candidates go deep into one component too soon… then run out of time with an unfinished design.
You can avoid this by structuring your discussion like an upside-down pyramid:
Start broad: Explore multiple solutions and trade-offs. Pick one.
Then go deep: Once the high-level design is clear, focus on key areas.
To give you an idea of how you should budget your time:
5 minutes clarifying the problem
10 minutes doing a high-level design
10-15 minutes doing a deeper design, refining, and getting feedback
Don’t let one detail derail you. If you get stuck, move on. And if you don’t know something, say so. Interviewers respect honesty and composure over guesswork.
Bottom line? Practice. A lot.
System Design success isn’t just about knowledge. It’s about clear communication, structured thinking, and leading the discussion. And the best way to improve? Practice, practice, practice.
Mock interviews help you get comfortable applying these strategies and simulate real conditions. The more you practice, the more natural it becomes.
I hope the tips I shared today help you refine your approach and walk into your next interview with confidence.
👉 Get more battle-tested tips and tricks in my free guide: The System Design Handbook.
Which topic would you like me to cover next? Hit reply or leave a comment to let me know.
Happy learning!