When a metric becomes a target, behaviour shifts and the number stops reflecting reality. Marketing is full of these traps.
When a measure becomes a target (and it will), then it stops being a good measure. That is the practical lesson of Goodhart’s law, and we see it everywhere.
We choose a metric because it is meant to reflect something real. Then we start managing to the number. People change behaviour to improve the score; the score rises. But the underlying reality? Probably not.
Marketing is especially vulnerable because so much of what we care about, like trust, is hard to measure directly. We reach for substitutes such as open rate.
If we optimise for email opens, we learn to write curiosity subject lines and send more often. The open rate trend looks great. But the real question was whether the email moved buyers closer to action.
Even traffic is a Goodhart trap.
If we target visits, we can publish broad content that ranks for low-intent queries. Sessions increase. Engagement falls. The site looks busy, but what about the revenue? We end up mistaking attention for demand.
A metric should help us make a decision. If it is not helping us decide what to do next, it is probably not the right one to obsess about.