Campbell's Law

NNGroup published this useful summary about the way focusing on metrics can be detrimental to teams, organizations, and their customers, especially when they're funneled into a single metric like in the North Star framework.

NN starts by arguing that the common saying "what can't be measured can't be managed" is a misquote, and that the actual quote is the polar opposite: "“It is wrong to suppose that if you can’t measure it, you can’t manage it – a costly myth.”

Campbell’s law states that the more important a metric is in social decision making, the more likely it is to be manipulated.

There's a similar saying by another social scientist:

Godhart’s Law states that “When a measure becomes a target, it ceases to be a good measure”

Both statements argue that single metrics can't substitute for holistic, complicated human behavior.
When humans are put in a situation where a metric is of high importance, they are very likely to modify their behavior in order to improve the metric, but this doesn't mean they'll act in a way that corresponds to the underlying intention or problem the metric is trying to solve.

There are many examples of this:

Schools that are optimized to getting students in college fail to make them truly expand student's potentials for knowledge and growth.
Customer service agents "cheating" by put customers on mute instead of on hold to improve their SLA metrics.
Businesses can pressure or reward customers for leaving positive reviews. So they're more interested in inflated reviews than actual feedback and improving the customer experience.

What can we do

Recognize that all metrics are flawed
Recognize that all metrics are biased and reflect what's important to the people setting them.
Combine metrics together to get a fuller picture of the experience.
Never rely on quantitative metrics alone. Triangulate research methods
Treat data as a tool for decision making, but do now allow them to make the decisions for you.