Ad fatigue occurs when a target audience has been overexposed to the same ad creative, causing engagement to drop, click-through rates to fall, and cost per result to rise. It is one of the most common reasons for Meta campaign performance deterioration, especially in retargeting campaigns with small audiences. The earliest warning signs are a rising frequency metric combined with a declining CTR and worsening ROAS. The fix is creative rotation, regularly introducing new ad variations so the algorithm has fresh signals to optimize from.