Why growth plateaus even when spend goes up

A plateau reads like market saturation. Usually it is arithmetic. If a system loses a fixed share of value at each transfer, then adding spend adds loss proportionally, and the visible output curve flattens long before demand does.

How to tell the difference

Saturation shows up as falling conversion at the top and stable conversion downstream. Leakage shows up as stable conversion everywhere and rising volume with flat output. The second is far more common and far more fixable.

Working the plateau

Stop testing creative. Take the three largest transfer points, measure records in versus records out, and price the delta. The plateau usually resolves into two or three specific, boring, closable gaps.