🔷 Things to AVOID in System Design Interviews

🧠 Core Truth

"Interview is NOT about perfect design — it's about HOW you think."

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❌ 1. Ignoring Requirements

Mistake

• Jumping into design without understanding problem

Fix (What to say)

"Before designing, I'd like to clarify requirements."

Example

Design Uber:

• ❌ Assume ride-sharing only
• ✅ Ask → pooling? payments? real-time tracking?

👉 Insight: Wrong assumptions = wrong system

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❌ 2. Going Too Deep Too Early

Mistake

• Starting with DB schema, APIs immediately

Fix

"I'll first define high-level architecture."

Analogy

🏗️ Building house:

• You don't start with wiring
• You start with structure

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❌ 3. Being Rigid (Big Red Flag 🚨)

Mistake

• Sticking to one idea no matter what

Fix

"We can also consider an alternative approach…"

Example

• You choose SQL
• Interviewer hints scale issue
• You should switch → NoSQL

👉 Insight: Flexibility = senior engineer signal

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❌ 4. Ignoring Trade-offs

Mistake

• Saying "this is best" without reasoning

Fix

"This approach improves X but compromises Y."

Example

• Cache → fast reads ✅
• But → stale data ❌

👉 Golden Rule:

"Every decision has a cost"

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❌ 5. Ignoring Non-Functional Requirements

Mistake

• Only talking about features

Fix

"Let's define scale, latency, and availability."

Example

• 10 users vs 10M users → completely different design

👉 Insight:

"Scale decides architecture"

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❌ 6. Poor Communication

Mistake

• Thinking silently / jumping steps

Fix

"Let me walk you through my thought process."

Example

• Don't just draw diagram
• Explain WHY each component exists

👉 Interviewer evaluates:

• clarity > correctness

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❌ 7. Not Engaging Interviewer

Mistake

• Treating it like a lecture

Fix

"Does this assumption sound reasonable?"

👉 Makes it collaborative

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❌ 8. Overconfidence / Bluffing

Mistake

• Acting like you know everything

Fix

"I'm not fully sure here, but one approach could be…"

👉 This is GOOD, not bad

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⚡ 9. Missing Estimation (Advanced Mistake)

Mistake

• Designing without numbers

Fix

"Let me estimate scale to guide design."

👉 Without this:

• You don't know if system will break

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⚡ 10. No Bottleneck Thinking

Mistake

• Happy path only

Fix

Ask:

"What will break first?"

Example

• DB overload
• Network bottleneck
• Cache miss storm

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🎤 Interview Script (Memorize This)

Start

"Before jumping into design, I'll clarify requirements and define scale."

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While Designing

"I'll start with a high-level design and refine it step by step."

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Decisions

"This approach improves X but comes with trade-off Y."

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Engage

"Does this direction align with expectations?"

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If stuck

"I'll make a reasonable assumption and proceed."

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🧠 Final Cheat Sheet

Mistake	Fix
No clarification	Ask questions
Early deep dive	Start high-level
Rigid thinking	Show alternatives
No trade-offs	Always justify
Ignore scale	Define NFRs
Silent thinking	Speak thoughts
No estimation	Do quick math

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💡 Golden Line

"A strong candidate doesn't just design — they justify, adapt, and communicate."