A practice prompt we wrote. No company or candidate report names it, so it carries no company tag.
How to answer
The question has two halves, and the second carries the answer: what you assumed, and what you built so a wrong assumption was cheap.
- Why the date could not move. Who set it and what missing it would cost. If it could have slipped, the story is weaker; say why it couldn’t.
- What was missing, and why you could not wait. The spec another team owned, the decision still being negotiated, the data that did not exist yet.
- The assumptions, counted and named. “I made three assumptions.” For each: how likely it was to be wrong, what being wrong would cost, and who you showed the list to at the time.
- The protection for each one. A check that would tell you early, with the date you would know. A design that made being wrong cheap: a mapping table instead of code, both options behind a flag, a manual fallback kept ready.
- What happened. Which assumption failed, and what its protection did. A story where one of them broke and the protection held is stronger than one where you guessed everything right.
- What you kept. The habit, in one sentence.
Match each protection to what being wrong would cost: a nightly check for an assumption that’s cheap to fix, a parallel run only for the one that would miss the date. Say who agreed to spend the time on each.
Say the assumptions as a list, out loud; the interviewer will write it down.
The trap is the stamina story: late nights, a good guess, a shipped project. It shows effort, not judgment. The other trap is naming assumptions you only recognized afterward. If you did not write them down at the time, say so, and say what you do now instead.
Follow-ups
What the interviewer may ask next, once your first answer is on the table.
- Which assumption were you least sure of, and why did you not wait for it?
- What did the protection for that assumption cost in time, and who agreed to spend it?
- If every assumption had held, would the protections have been wasted effort?
Where answers go wrong
- Tells a story in which the speaker worked late, guessed right and shipped, which shows luck and stamina but no method for being wrong.
- Lists assumptions in hindsight that were never written down, checked or given a fallback at the time.
Answer this in two minutes
Write the answer you would say out loud. The clock starts with your first word.
Illustrative answer about a fictional project
I led the integration between a hospital network’s nurse-scheduling system and its new payroll provider. The old payroll contract ended on 31 December, and the first payroll on the new system ran on 9 January.