Not knowing isn't failing
Every interview has a question you can't answer. That's expected — interviewers often probe for the edge of your knowledge on purpose. They grade not whether you have a ready answer, but how you behave at that edge.
What to do
Admit it honestly, but don't give up. "I haven't worked with this specifically, but let me reason about it." This defuses the tension and keeps trust.
Reason from first principles. Tie the unknown to what you know: "I haven't set up Kafka itself, but from working with queues I'd expect partitioning and delivery guarantees to be the key concerns."
Show where you'd look. "I'd start with the docs on section X and test the hypothesis on a small prototype." That demonstrates a working process, not memorization.
What not to do
- Bluff. An experienced interviewer will catch the fabrication, and trust drops harder than from an honest "I don't know."
- Go silent and quit. Silence reads as "nothing to offer."
- Apologize in a loop. One "haven't run into this" is enough — then move to reasoning.
The answer formula
- Honestly mark the boundary.
- Connect it to what you know.
- Propose how you'd figure it out.
Checklist
- I admit gaps calmly, without panic
- I connect the question to nearby experience
- I narrate how I'd find the answer
- I don't bluff or invent