Economics
Goodhart's Law and the Pitfalls of Metric-Based Governance
Quick fact
In the Soviet Union, a factory was rewarded for producing a target number of nails, so it produced thousands of tiny, useless nails; when the target switched to weight, it produced a single giant nail.
Why this is interesting
You set a goal to lose 10 pounds, but the scale barely moves while your jeans fit perfectly. Why did your metric betray you?