---
title: '5 Critical Mistakes to Avoid in System Design Interviews'
source: 'https://youtube.com/watch?v=OvufRkoD-D0'
video_id: 'OvufRkoD-D0'
date: 2026-09-03
duration_sec: 408
channel: 'ByteByteGo'
---

# 5 Critical Mistakes to Avoid in System Design Interviews

> Source: [5 Critical Mistakes to Avoid in System Design Interviews](https://youtube.com/watch?v=OvufRkoD-D0)

## Summary

System design interviews can make or break your chances at top tech companies, and even well-prepared candidates often stumble on common pitfalls. This video outlines the five most critical mistakes that can tank a system design interview and provides actionable advice on how to avoid them.

### Key Points

- **Mistake 1: Not Thinking Out Loud** [00:17] — Candidates who design silently fail to show their thinking process. Interviewers evaluate communication and collaboration skills, not just technical ability. Always narrate your thought process and discuss trade-offs.
- **Mistake 2: Skipping Requirements Clarification** [01:15] — Jumping straight into design without clarifying requirements is a major error. Different systems have vastly different needs. Always ask about functional and non-functional requirements, and document assumptions.
- **Mistake 3: Diving into Details Before Architecture** [02:28] — Discussing implementation details like encoding formats before establishing the overall architecture is backwards. Start with the big picture: major components, relationships, and data flow, then dive into specifics.
- **Mistake 4: Ignoring Trade-offs** [03:42] — Every design decision involves trade-offs. Present multiple options, explain the pros and cons, and make a recommendation. For example, WebSocket offers low latency but adds complexity compared to HTTP polling.
- **Mistake 5: Over-engineering** [05:01] — Over-engineering for the given scale is a common mistake. For 1,000 URLs per day, a simple web server with a single database is sufficient. Start simple, then discuss scaling strategies as requirements grow.

### Conclusion

System design interviews test your ability to solve ambiguous problems under time pressure. There is no perfect solution—every design involves trade-offs. Your job is to understand requirements, propose a reasonable solution, and clearly explain your reasoning. Practice these patterns to avoid common mistakes and be well-prepared.

## Transcript

System design interviews can make or break your chances at top tech companies. Even well-prepared candidates often stumble on common pitfalls that are easily avoidable. Today we will look at 5 most critical mistakes that can tank your system design interview and how to avoid them.
You are designing a social media feed. You start drawing components and connections that work silently. The interviewer has no insight into your thinking process. System design interviews evaluate both your technical skills and your ability to communicate and collaborate.
The six. Think out loud. Narrow your thought process. I'm considering two approaches for feed generation. Push-based pre-compute feeds when users post. Pull-based compute feeds on request.
Discuss your reasoning. Push is faster for reading but expensive for popular users with millions of followers. Pull is slower but more efficient for storage. Engage your interviewer. Given these trade-offs, which approach seems more suitable for our requirements?
Ask for feedback. Does this design address the main concern? Are there constraints I should consider? This demonstrates collaboration skills that are essential for senior engineering roles.
Now, even if you communicate well, you can still fail by making a mixed mistake. The interviewer asks you to design a URL shortener. Many candidates immediately thought, we need a load balancer, web servers,
routers for caching, and a hash function for generating short URLs. This is wrong. You are designing a system without understanding the requirements Different URL shorteners have vastly different needs Is this for internal use or public internet Do you need analytics Custom URLs What the expected scale Without
clarifying requirements, you might build a wrong system entirely. The fakes start with questions. Always. Ask about functional requirements. What features do we need? Who are the users?
What's the expected usage pattern? Ask about non-functional requirements. How many URLs per day? What's the read-to-write ratio? Any latency requirements?
Document your assumptions. If the interviewer doesn't specify something, state your assumption clearly. This shows you understand the system design is about solving real problems. But asking the right questions is only the beginning.
A certain mistake happens when you start designing. You are designing a video streaming service. Requirements are clear. The candidate immediately discusses video encoding formats, CDN configurations, and compression algorithms.
This is backwards. You are diving into implementation details before establishing the overall architecture. The fakes start with the big picture. Begin with major components. We need an upload service for content creators, a processing service for video encoding,
storage for video files, and a streaming service for viewers. Show the relationships. User uploads through our API, videos get queued for processing, processed video go to distributed storage,
and streaming happens through our CDN. Walk through the flow. A creator uploads a video it gets encoded into multiple formats stored across regions and served to viewers based on their location and device Only then dive into specific components
This shows you can think systematically about complex problems. Once you have a solid high-level design, you need to show technical depth. This is where a fourth mistake often occurs.
You are designing a chat application and discussing how to handle message delivery. The candidate sets will use WebSocket because they are real-time. No explanation, no discussion of what you're giving up.
Every system design decision involves trade-offs. Choosing WebSocket gives you low-latency real-time communication, but you lose simplicity and have to handle connection management complexity.
The fakes always discuss trade-offs, present multiple options. For message delivery, we have two main approaches. HTTP polling is simple and works through firewalls and proxies easily.
WebSocket provides true real-time communication with low latency. Explain the trade-offs. HTTP polling is simple to implement but wastes resources with frequent requests.
WebSocket provides real-time communication with minimal overhead but requires handling persistent connections and is more difficult to scale. Make a recommendation. Given the requirements for real-time chat with potentially thousands of concurrent users,
I would choose WebSocket. This shows you understand that engineering is about making informed choices between competing priorities. Our final mistake is about judgment and scale.
You clarified the requirements The URL shortener needs to handle 1000 URLs per day The candidate responds we use microservices for scalability implement database sharding deploy across
multiple regions with a CDN. This is a massive over-engineering. 1,000 URLs per day is roughly one every 90 seconds. A simple web server with a single database can handle millions
of operations per day. To fix, start simple, then scale. For a thousand URLs per day, begins with a basic architecture. Single web server, single database,
simple hash function. This handles the requirements with minimal complexity. Then discuss scaling. As we grow to a hundred thousand URLs per day, we might add caching. At millions per day,
we'll consider database shorting. This demonstrates you understand the relationship between scale and complexity. You can design for growth without unnecessary early optimization. System design interviews test your ability
to solve ambiguous problems under time pressure. There's no perfect solution. Every design involves trade-offs. Your job is to understand requirements, propose a reasonable solution,
and clearly explain your reasoning. Practice these patterns, avoid these common mistakes, and you will be well prepared for your next system design interview. Want more content like this? We'll build your one-stop resource for technical interview prep.
From system design to coding challenges, behavioral tips to ML concepts, it's all there. One subscription, complete access. Get 50% off at bytebytego.com.