Your board deck has a slide with blended ROAS on it. You didn't build that number, someone on the data team pulled it from three different exports last Tuesday, and if it's wrong, nobody's going to blame the spreadsheet. They're going to blame you.

That's the uncomfortable part of what CMOs should know about ecommerce analytics: you're accountable for numbers you don't actually control the pipeline for. Marketing sets the budget. Finance and data teams decide how that spend gets attributed, cleaned, and reported back. Somewhere in that handoff, a lot gets lost, and it usually surfaces at the worst possible moment, in front of the board.