The attempt to assign credit for a sale to the marketing touchpoints that drove it. Attribution is necessary and permanently imperfect: every platform over-claims, last-click ignores everything that built demand, and privacy changes keep eroding the data. Use it directionally to allocate budget, but anchor decisions on blended MER and incrementality, not on any single model's tidy numbers.
Benchmark. If your platforms' attributed revenue sums to more than your actual revenue, the over-claim is the gap. Trust MER as the source of truth and use attribution to decide where to lean in.