Great example of Goodhart:

I used to work at a Verizon store, and we were rated by the amount of accessories we could sell with each phone. In order to boost that number, everyone tried to add on a bunch of cheap phone accessories (clearance items and screen protectors) to drive that number up.

Our goal was more than three, but once we figured out how to sell 5 or more for less than $20, they changed it to total cost of accessories per phone.