The Bounty That Bred the Rats

Every number you chase is quietly drifting away from the thing it was supposed to measure.

In 1902, Hanoi paid one cent per rat tail. Within months, the city was overrun by rats with no tails.

The bounty was Paul Doumer’s idea. Doumer was the governor-general of French Indochina, and he had just built a modern sewer system under Hanoi as a monument to colonial engineering. The sewer was a wonder. It was also, as the historian Michael Vann documented in his 2003 paper “Of Rats, Rice, and Race,” one of the greatest rat habitats the city had ever produced. Plague broke out. Doumer offered one cent per tail. On a single day in June, more than twenty thousand tails were turned in.

Then someone noticed the rats.

Tailless rats running through the streets. Tails being smuggled into Hanoi by the hundreds from villages where the locals had set up small rat farms in their apartments. They had figured it out faster than the colonial government. You can have the tails without giving up the rats. Snip the tail. Let the animal go. Wait for it to breed. Collect again.

The bounty did not eliminate the rats. It paid for their cultivation.

What Goodhart Named

In 1975, an economist named Charles Goodhart wrote a paper called “Problems of Monetary Management: The U.K. Experience.” In a footnote, he stated a principle that came to be called Goodhart’s Law. Any observed statistical regularity, he wrote, will tend to collapse once pressure is placed upon it for control purposes. The Bank of England was targeting a money supply number called M3, and the moment they targeted it the banks rearranged their balance sheets so M3 went up without anything else changing.

In 1997, the anthropologist Marilyn Strathern compressed the idea into the line most of us know. When a measure becomes a target, it ceases to be a good measure.

Read it twice. The thing you measure was supposed to be a proxy for the thing you actually wanted. The proxy and the prize were never identical. The moment you start chasing the proxy, it stops behaving like a proxy and starts behaving like a slot machine.

Rats grew tails so they could be cut off. M3 went up so the Bank of England would relax.

The Version You Are Running

You do not run a rat farm. You run something quieter.

You wear a watch that counts steps, and last week you walked an extra mile because the watch said you were two hundred steps short. The watch did not know you walked the mile in circles in your living room. You check a screen time report and you spent two hours less on your phone this week, but the way you got there was by reading the news on your laptop instead. Your weekly review shows nine deep work hours and you cannot remember producing anything from any of them.

The dashboards do not care whether the underlying thing is improving. They care whether the number is.

A friend of mine has not missed a workout in two years. He is also weaker, slower, and more injured than he was when he started. The number stayed perfect. The thing the number was measuring quietly walked off.

Most of what we call discipline is the discipline of moving a number. Most of what we call discipline is rat tails.

The Inversion

Stop looking for cleaner metrics. There is no number clean enough to survive being aimed at.

The real move is older and harder. You have to keep two things in your head at once. The number, and the thing the number was supposed to be a proxy for. You have to check the thing against itself, not against the dashboard. You have to ask, every so often, whether the work counts.

The colonial government in Hanoi could not do this because they had never had to live with rats. They had a budget and a problem and a measurable outcome. The locals had a city. The locals could see the rats were not going down, that the streets still ran with them, that the bounty had become a side hustle. The locals lived inside the thing the metric was supposed to track.

Most of us do not. We are tourists in our own lives, looking at the dashboard from somewhere above the ground.

How to Catch Yourself

Three moves.

First, name what the number is for. Write one sentence that says what the metric is a proxy for. “Steps are a proxy for being someone who moves through the world easily.” “Words written are a proxy for being someone with a habit of thought.” Pin it where you will see it. When the metric and the thing drift apart, you want to catch the drift early, before the metric becomes the prize.

Second, schedule unmeasured time. One day a week, do the thing the number is a proxy for without checking the number. Walk without the watch. Write without the word count. Talk to someone you love without thinking about how to phrase it for an audience. The capacity to do the unmetered version of the thing is the capacity that will carry you when the dashboards break.

Third, run an honesty audit on your own gaming. Every Sunday, ask: what did I do this week purely to move a number? Cancel one of those things. Replace it with the unmetered version. Watch your own mind resist. The resistance is the data.

The Tails Were Not the Trap

The Hanoi locals did not break the colonial bounty out of malice. They saw the system clearly and they ran the play. The tails were never the problem. The problem was that the people designing the system never lived in the city.

The same is true of every dashboard you have built for yourself. Aim at the measure and you miss the meaning. Cut the tail and the rat runs free. The number was never the thing.

Go check on the thing.