Advertising that performs well initially tends to weaken over time even when nothing about the targeting or budget changes. The audience has seen it, and repetition changes how it is received.
Repetition moves from recognition to disregard
The first exposures to a message do useful work, establishing what is being offered and by whom.
After several more, the audience recognises the advertisement quickly enough to skip it, and recognition becomes a mechanism for avoidance rather than attention.
Response rates fall while the advertisement is still being delivered as intended, which is why the decline shows in results before it shows in delivery data.
A narrow audience fatigues faster
Tightly targeted campaigns reach a small group repeatedly, so the average number of exposures per person rises quickly at any given budget.
The same spending across a broader audience accumulates exposures more slowly, which extends the life of the creative at the cost of some precision.
This is why highly targeted campaigns often perform excellently for a short period and then deteriorate sharply, while broader ones decline more gradually.
Increasing budget accelerates the decline
The natural response to a campaign that is working is to spend more on it, which increases how often each person sees it.
Where the audience is finite, additional budget buys additional frequency rather than additional reach, and frequency is what causes the fatigue.
Scaling a successful campaign therefore requires either a larger audience or new creative, since more money against the same combination shortens the campaign's useful life.
Refreshing is not the same as replacing
Changing the visual treatment while keeping the underlying argument often restores some performance, because the recognition trigger has changed.
Replacing the argument entirely is a different exercise, and it discards whatever the previous message had established in the audience's memory.
Advertisers who rotate variations of a working idea generally sustain results longer than those who start again each quarter with something new.
Fatigue is a property of the audience, not the advertisement
The same creative can perform well in a market where it has not run before while failing in one where it has been saturated.
Treating performance as a property of the message alone leads to discarding work that is still effective for people who have not seen it.
Separating the two lets an advertiser retire a campaign in one place and continue it in another, which is a cheaper position than constant replacement.