I just can't find the Wiki page on it, but there is a great "rule" out there: As soon as you tell people what they are getting measured on they will put their whole energy into gaming the measurements to their advantage.

I'm guessing you're thinking of this: https://en.wikipedia.org/wiki/Campbell%27s_law

(See also, https://en.wikipedia.org/wiki/Campbell%27s_law#Similar_rules)