Myth: feed your native platform conversion data and lookalikes will scale your wins.

Myth: feed your native platform conversion data and lookalikes will scale your wins.
No — watch what actually happens. A merchant fed purchase events into a native platform's optimizer. Weeks 1–3: cost-per-sale fell from $30 to $19. Lookalikes working, supposedly.

Weeks 4–8: the algorithm, optimizing for the cheapest conversions, drifted hard toward existing customers and coupon-hunters — people who'd have bought anyway. Incremental new-customer cost, measured by holdout, rose to $74.

The dashboard cost-per-sale kept falling. The incremental cost-per-new-customer kept rising. They moved in opposite directions.

The optimizer doesn't maximize your business; it maximizes the metric you handed it. Hand it "any conversion" and it'll proudly re-sell you your own buyers. Are you measuring incrementality, or applauding cannibalization?