about a year ago i wrote a short post on measuring KPIs... up to a point, where i've compared KPIs to Heisenberg's uncertainty principle. today i've learned it's actually formalized and beautifully put by Goodhart's law:
Any observed statistical regularity will tend to collapse once pressure is placed upon it for control purposes.
and Marilyn Strathern's generalization of it:
When a measure becomes a target, it ceases to be a good measure.