You never observe demand. Train on what?
Causal inferenceHardProblem. Your training label is units sold. But if an item stocks out on Tuesday, Tuesday's sales are zero and demand was not. Roughly 5% of item-days have a stockout. A colleague says 5% is small enough to ignore. Is it?
Before you reveal: say your answer out loud, as if you were in the real interview — get your reasoning across clearly first. There is no single correct answer: reading what the interviewer is really after and defending your own thinking is what makes an answer strong.