The Project Deep Dive

Intermediate · 14 min read · Behavioral Interviews Decoded, The Questions Everyone Gets

Pick the right project and survive twenty minutes of "why" questions about it.

Sooner or later an interviewer says, "Tell me about a project you're proud of", and then keeps asking "why?" for twenty minutes. The project deep dive tests two things at once: whether you really did what your resume says, and how deep your technical judgment goes.

Choose the right projects

Cracking the Coding Interview advises mastering two or three projects, chosen because:

Prepare these answers for each project

For each project, prepare the answers to these questions in advance. The book lists challenges, mistakes, technical decisions, technology choices and trade-offs, and what you'd do differently; scaling questions are common follow-ups.

The structure of a good deep dive

Here's how a decision sounds when explained well:

Questions you'll get, and what they're testing

Experienced candidates are held to a higher bar here. The book notes that an experienced engineer's answer to "what was the hardest bug you've faced?" is expected to be more in-depth and impressive.

Interview questions

How do you talk about a project where most of the work was done by others?

Key takeaways

Master two or three projects where you had a central role on the challenging parts.
Prepare the problem, your role, the architecture, key decisions with alternatives, the hardest part, mistakes, results, what you'd do differently, and scale.
Overview first, then let the interviewer steer; go deep on decisions and trade-offs.
Be exact about your own contribution; overclaiming is exposed by follow-ups.

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