Goodhart's law, although it can be expressed in many ways, states that once a social or economic indicator or other surrogate
measure is made a target for the purpose of conducting social or
economic policy, then it will lose the information content that would
qualify it to play that role. (Wikipedia)
and to paraphrase... if attention is focused on a particular outcome then that outcome becomes useless as a measure of performance.
In the arena of social and/or economic policy, this can be because people 'game' to optimise the outcome that is the focus of attention, eg; hospital waiting times.
