When a measure becomes a target, it ceases to be a good measure ~ Charles Goodhart (1975). Problems of Monetary Management: The U.K. Experience. In Papers in Monetary Economics (Vol. 1). Reserve Bank of Australia.
Once a metric is singled out as the primary goal or performance standard, people will optimize for that metric in ways that may undermine its usefulness or distort the system it is meant to measure. This is part of the reason why so much of what actually works in the field of finance is counterintuitive. This video is an excellent resource because it covers a vast array of misconceptions in finance that are very costly to a large percentage of people.
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