Handling Unknown Questions in Interviews

Almost every technical interview eventually includes a question you cannot answer from memory. It might be about a system you have never built, a customer situation you have never handled, or a tradeoff you have never had to weigh. In that moment you may have nothing to recite. This article looks at what to do next, and at a belief that quietly pushes many candidates toward the wrong move.

The short version is this: state honestly that you have not seen the specific case, then reason about it out loud. The rest of the article explains why that works, what the reasoning should contain, and how the moment unfolds from the interviewer's side.

A common belief goes like this: if I admit I don't know, the interviewer will mark me down, so I should produce a confident answer even if I have to improvise it. The instinct is understandable. It treats the interview as a scoreboard where every visible gap is a point lost.

The belief is worth examining before accepting it. The useful question is not whether a gap looks bad on the scoreboard but what the interview is actually measuring. Once you answer that, the case for improvising weakens considerably.

The source makes a specific claim here: an interview is not a knowledge test but a thinking test. If the purpose were to check how much you have memorized, a bluff might pass. Because the purpose is to see how you think, a made-up answer gives the interviewer almost nothing to evaluate. A fabricated answer hides the very thing being measured, which is your reasoning.

Seen this way, an unknown question is not a trap that exposes a missing fact. It is an opportunity. The interviewer has given you a problem whose answer you do not have, which means the only thing left to observe is how you approach it. Your recall of a fact can be checked against a reference. Your reasoning on an unfamiliar problem can only be seen when you speak it.

The source recommends a response that is short and consistent, and it has two parts. The first is an honest statement that you have not encountered that specific case. The second is a signal that you are about to reason, such as saying you would approach it by working through the problem.

After the honest opening, the source describes what reasoning from first principles looks like when spoken aloud. It names three elements: the assumptions you would test, the people you would consult, and the experiments you would run. Each one turns an unknown into a plan.

Together the three elements demonstrate judgment even when the specific answer is missing. The interviewer can evaluate each one: whether your assumptions are sensible, whether your choice of people reflects how knowledge is spread through an organization, and whether your experiments would turn uncertainty into evidence.

The two paths are easiest to compare side by side. The honest path names the gap and then exposes assumptions, people, and experiments, all of which the interviewer can evaluate. The bluff path produces a confident sentence that leaves the reasoning out of view.

Bluffing tends to lose more often than naming a gap, for two reasons the source gives. First, a bluff hides the reasoning, which is the thing the interview is designed to see. Second, the bluff is detectable. Once the interviewer asks a follow-up question, the improvised answer tends to fall apart, and the credibility lost is usually greater than the gap that was honestly named.

Follow what the interviewer knows at each moment in a realistic exchange. The state below is generated for illustration and is not drawn from a specific source case. Notice that the interviewer's picture of you changes with every move, even though no fact has been checked.