One of the more interesting aspects of economic policy is the "unintended consequences" aspect. An action is taken, a result is achieved (to degree lesser or greater than expected), but there follows an unintended consequence. Pundits like to take shots, saying that certain consequences should have been foreseeable and should have been taken into consideration when the policy was first formulated. I tend to agree that certain consequences are foreseeable (especially with a little economic thinking). But, if you'll forgive the cliché, only hindsight is 20/20.
That being said, here's an interesting story from The New York Times last month. (HT to Izzit). It seems that authorities, in effort to forestall the spread of swine-flu, ordered the killing of all pigs. I suspect that policy-makers in most countries would likely not have foreseen this outcome.
Regardless, it makes an excellent example when discussing those “unintended consequences.”