Amnesia, and what it does not forget
Traditional marketing mix modelling is built on time. This is built on relationships,
and one mechanism is responsible for the difference. We call it Amnesia.
The network wakes up at the start of every row with no memory of the row before it. It
sees a set of input values, sees the revenue they should account for, notices the gap,
and nudges its weights to close it — in small steps, inside geometric constraints. Every
week is a state of the world to be explained on its own terms, not a point on a line
inherited from the week before.
The precision matters here, because this is where the idea is usually misread:
the amnesia applies to the weights, not to the inputs. Adstock has
already folded the time-echo of previous weeks into the independent variables — the
residual awareness a placement leaves behind is sitting right there in the row. So the
model keeps the benefit of time without inheriting the constraint of chronology.
Which is also why the training data is walked in order from a random starting point
rather than shuffled outright. The rows are not strictly independent: adstock decay
links each one to the ones before it.