In one line
Show the same people the same creative long enough and response cools. Frequency climbing while CTR falls — that scissor shape — is the fatigue signal.
Separating it from other causes
A falling CTR makes you want to swap creative immediately. Check frequency first.
- Frequency ↑ with CTR ↓ → fatigue is likely. Rotate creative or widen the audience.
- Frequency flat with CTR ↓ → probably not fatigue. Look at competition, season, targeting changes. New creative will not fix this one.
A drop in blended CTR is also frequently just a larger mix of new assets still in learning.
When rotating
Swapping every underperformer at once destabilises learning. Replace the bottom few instead.
Go deeper
Rotation priority and test design are covered in ad creative testing.