Tell me about a mistake that cost the company money.
What they are really testing: Whether you can discuss financial impact without deflecting, and whether you think about cost as an engineering property rather than someone else problem.
A real interview question
Tell me about a mistake that cost the company money.
What most people say
drag me
“I once left some instances running but finance spotted it on the bill and we shut them down.”
No number, no ownership, and the detection was someone else noticing a month later. It also shows no curiosity about why nothing alerted, which is the actual engineering lesson.
The follow-ups they ask next
How would you stop this class of thing generally?
Ephemeral environments with automatic expiry, mandatory tagging with an owner and a TTL, a scheduled sweep for untagged or expired resources, and anomaly alerts on daily rather than monthly spend.
Whose responsibility is cloud cost?
Engineering, because engineers create the spend and only they can change it. Finance can report it but cannot fix it. Cost is a non-functional requirement like latency.
What the interviewer is listening for
- Gives the actual figure
- Identifies the missing feedback loop as the real defect
- Guardrail later caught someone else mistake
What sinks the answer
- Avoids the number
- Blames the absence of process
- No systemic fix
If you genuinely do not know
Say this instead of freezing. Reasoning out loud from what you do know beats silence every single time, and a good interviewer is listening for exactly that.
“I [did X], which cost [specific figure] over [time] before [how it was caught, honestly]. I [owned it publicly straight away]. The real defect was [the missing feedback loop, not just my error]. So we [added the systemic guardrail], which [later caught something else].”
Keep going with behavioural
Mid
Tell me about a time you broke production. What happened and what did you do?
Mid
Tell me about a time you disagreed with a developer about how something should be deployed.
Mid
Tell me about a time you were on call and it went badly.
Mid
Walk me through a time you inherited a system nobody understood. Where did you start?
Mid
Tell me about something repetitive you automated. How did you decide it was worth it?
Mid
Tell me about a time you did not know something important and had to act anyway.
Knowing the answer is not the same as recalling it under pressure
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