That is from Friedrich Hayek's Law, Legislation, and Liberty via Cafe Hayek (HT to Bill Easterly). The full post is worth reading for a quick summary of some of Hayek's key insights. Among them is this: that rules, laws, regulations, institutions, etc were generally not invented by specific people or by a society for specific purposes. Hayek's point is that in most cases they actually evolved organically.
A corollary is as follows: Being able to describe (a) how a system currently does function and then (b) how it should function generally does not (c) lead to the system getting changed.