After conducting 100+ interviews as a hiring manager at a FAANG company, I want to share an observation about what separates candidates at the senior level.

For junior to mid roles, coding ability is the primary signal. Can you solve problems? Can you write clean code? Can you analyze time complexity?

For senior+ roles, the coding bar is still there, but the differentiator is system design. Here's why:

1. Senior engineers spend most of their time designing systems, not implementing algorithms
2. System design reveals how you think about tradeoffs, which is the essence of engineering
3. It shows whether you have practical experience or just theoretical knowledge
4. It tests communication skills, which matter more at senior levels

I've seen candidates who aced all coding rounds but gave shallow system design answers. They often get hired at a lower level than they expected.

Conversely, I've seen candidates who struggled with a hard coding problem but gave an outstanding system design interview. They often get the strong hire at the target level.

This isn't to say you should neglect coding prep. You still need to clear the coding bar. But if you're preparing for a senior role and have limited time, invest more heavily in system design.

I recommend being able to design 10-15 different systems from scratch, with deep knowledge of 5-6 of them.