Realized halfway through a system design round I was designing for a scale nobody mentioned and had to walk it back live

Heard "high traffic" in the prompt and immediately went to sharding and a message queue, the whole distributed-systems playbook. Ten minutes in the interviewer gently asked what scale I was actually assuming, and it turned out to be maybe a few thousand daily users. Had to backtrack the whole design in front of them. Weirdly, being willing to say "I over-engineered this, let me simplify" out loud seemed to land better than if I'd guessed the scale right from the start.