Establish which constraint it is
- Conversion rate too low → page, price or offer.
- CPC too high → relevance or auction competitiveness.
- AOV too low → bundles, thresholds, upsells.
Then try one change
Marginal products fail because people change everything at once and never learn which lever mattered.
And set a deadline
Decide in advance what result, by when, keeps it alive. Without that, marginal products absorb budget indefinitely because nobody wants to make the call.