Economist Charles Goodhart proposed the following rule in a 1984 article: "Any observed statistical regularity will tend to collapse once pressure is placed upon it for control purposes."'
The statement is applicable in many places beyond statistics, of course, which the anthropologist Marilyn Strathern pointed out in her 1997 paper: "When a measure becomes a target, it ceases to be a good measure."
This observation is worth keeping in mind every time we try to measure something with a goal in mind.
The number on the scale does not necessarily reflect your overall health.
The number of likes your brand has on social media isn't necessarily a measure of its success.
The number of books you read in a year doesn't necessarily represent how much you've learned.
Another example: When you put pressure on the police to reduce crime, they may discover that it's easier to simply downgrade the severity of reported crimes than to address the systemic problems that lead to them in the first place.
It's often hard to know if we're making progress towards something without measuring it. But as Strathern so insightfully noted, once our goal is a number, the strategies we have for reaching that number may distract us from our actual goal.