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Past Project Deep Dive: Technical Trade-offs and Handling a Technical Disagreement

InstacartSoftware Engineer · Technical Screen
MediumSoftware EngineerTechnical ScreenBehavioral & Leadership

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A behavioral round built around a past project: walk through it, explain a significant technical trade-off and why you chose it, and describe how you handled a disagreement over a technical decision. It tests ownership, decision-making with evidence and collaboration, rewarding specific detail over general statements.

This round centered on a project from your past work. The interviewer asked about the technical trade-offs you made in it and about how you handled situations in which someone disagreed with you.

Clarifying Questions

  • Should the disagreement come from the same project, or can it come from another one?
  • Is the interest in disagreements with peers, with a manager, or with another team?
  • How much technical depth is expected: architecture-level decisions, or details down to data structures and code?

Part 1 — The project and a technical trade-off

Walk through a project you worked on: the problem, your role and the system you built. Then explain one significant technical trade-off you made in it: the options, how you chose, and what the choice cost.

What This Part Should Cover

  • The problem, the scale and your personal contribution, kept brief
  • The options, the criteria and the evidence behind the choice
  • The cost of the choice, how it was contained, and the measured result

Part 2 — When someone disagreed with you

Describe a time when you and someone else disagreed about a technical decision. How did you handle it, and how was it resolved?

What This Part Should Cover

  • The decision at stake and both positions, stated fairly
  • How the disagreement was resolved: criteria, evidence, and who decided
  • The outcome, the working relationship afterwards, and what you learned

Hints

Hint 1

Pick a decision that cost something: Choose a decision in which the option you rejected had real advantages, so that you can explain what you gave up, why it was worth it, and how you knew.

Hint 2

Make the other side's case: Be ready to state the other person's position in its strongest form and to say what would have changed your mind.

Follow-up questions

  • With twice the traffic, would you make the same trade-off today?
  • What was the strongest argument against your choice, and who made it?
  • Tell me about a time you were the one who was wrong in a technical disagreement.
  • How did you explain the trade-off to people outside engineering?