The rat tail in your dashboard

Goodhart’s law is one of those ideas that quietly explains everything that feels a bit off in marketing. Coined by British economist Charles Goodhart, the law states: “When a measure becomes a target, it ceases to be a good measure.” In other words, the moment you start chasing the number, the number stops telling you the truth. It becomes a performance. A growth hack. Something that looks like progress but tells you very little about the real world.

In marketing, we see it all the time. You set a goal, boost engagement, increase conversions, lower cost per click, whatever. You watch your media team or performance agency work their magic. Until one day, you look at the results and wonder: “Wait, is this actually working? Or are we just getting better at gaming the metric?”

The Hanoi Rat Problem

There is a story behavioural economists (and myself) like to tell. It takes place in colonial Hanoi. The French administration had a rat problem. So they introduced a bounty system: bring in a rat’s tail and get paid. It worked, at first. Tails poured in. But strangely, the rats didn’t disappear. In fact, there were more of them.

What happened? People had figured it out. Cut off the tail, release the rat, let it breed, repeat. Some even started rat farms. The measure (rat tails) had become a target and in doing so, lost its connection to the actual goal (fewer rats). It’s the textbook example of Goodhart’s law in action: incentivize the wrong signal, and you get exactly what you asked for and nothing you actually need.

Engagement isn’t always engagement

Fast forward to today. A marketing manager wants higher engagement. The team and the agency get to work: memes, contests, giveaways. Tag three friends and win a tote bag. Like this post to unlock a surprise. Suddenly, the numbers are beautiful. Engagement is up 120%. Everyone’s happy.

Until you look closer. The comments are empty. The shares are forced. No one remembers what they reposted or liked a week later. You’ve optimized for a metric that no longer tracks what you thought it did. Just like rat tails, “engagement” stopped measuring true interest and started measuring tricks.

Clicks, opens, and other vanity metrics

Email campaigns fall into the same trap. You want more opens, so you A/B test your way into subject lines that scream “You won’t believe what happened!” People click, sure. But the body of the email is a letdown. You tricked the metric. And next time, fewer people will trust you. Open rates went up. Brand equity went down. You’ve met the target, but you’ve lost the story.

Or consider website traffic. You start pumping out SEO content. Fast, shallow, but keyword-rich. Google rewards you. Your sessions spike. But users bounce in seconds. They came, they clicked, they left. You hit the number. You didn’t move the needle.

The danger of hitting the wrong goals

The problem with Goodhart’s law is that it doesn’t announce itself. It’s a slow distortion. A gradual divorce between the number and what the number used to mean. You think you’re improving, but really, you’re just getting better at making the dashboard blink green.

And the longer you run on this illusion, the harder it becomes to change course. Because your team is chasing the bonus. Your agency is chasing the report. Your boss is chasing the slide deck. Everyone wants the number to go up. No one asks if it still matters.

So, what should marketers measure?

Here’s the hard truth: no metric is safe from Goodhart’s law. But that doesn’t mean we should abandon measurement. It just means we need to stay alert. Stay skeptical. Ask better questions.

What story does this number tell me? And what story could it be hiding?

It means putting brand health next to campaign performance. Looking at second-order effects instead of chasing instant feedback. It means recognizing that real marketing outcomes don’t always show up in this month’s report. But they’re the ones that shape next quarter’s success.

Marketing is part math, part art

Goodhart’s law reminds us that marketing is not a numbers game. It’s a behavior game. It’s painted in bright colours and draws attention to a message. And the moment we treat metrics as truth instead of signals, we start building campaigns for the spreadsheet and not for the audience.

The dashboard is not the market. And if you forget that, you’ll end up celebrating engagement that means nothing, conversions that cost you more than they make, and brand awareness that no one can remember.

The rats will still be there. You just won’t see them. Only the tails.