"What Is the Grain of This Table?"

Grain is not a modeling step. It is THE modeling step. Everything else follows from it: which columns belong in the table, which joins are valid, which aggregations produce correct numbers. Getting grain wrong does not produce an error message. It produces wrong numbers that look right. That is why interviewers test it. What They're Really Testing The 60-Second Framework Step 3 is the strong-hire signal. Asking the interviewer a clarifying question about grain shows you have been burned by wrong assumptions in production. Junior candidates never ask. Senior candidates always do. Grain Statements: Good vs Bad Why Companies Care Cite these in your answer: At Meta, wrong-grain caused ad revenue to be double-counted across ad groups for a quarter. At Amazon, order-level grain instead of item-l