To paraphrase Donald H. Rumsfeld, there are things that we know we know, and things that we know we don't know. But a third category keeps cropping up: things that we think we know, but don't really. A recent case in point involves smoking, obesity and health care costs.
Smokers and the obese are a drain on the health system because they require more medical care - right?
Wrong, according to a Dutch study published online last week in the Public Library of Science Medical Journal.
Healthy people tend to live longer, and as a result they consume more goods and services (including health care resources) than their nicotine-addicted and overweight peers. This conclusion "throws a bucket of cold water onto the idea that obesity is going to cost trillions of dollars," Patrick Basham, a Johns Hopkins University professor of health politics, told the Associated Press.
It's an obvious point, really - one we all probably should have realized before. But it flies in the face of one of the main reasons we slap ever-higher taxes on cigarettes.
Ah, unintended consequences. Once you start looking for them, they're everywhere.
Indeed, the entire field of medicine sometimes seems to be all about unanticipated results. Just last week, it was announced that researchers who expected to reduce heart attack deaths among diabetics by lowering their blood-sugar levels had to stop doing that - patients were dying because of it.
Who would have thought? And yet we've long known that every medication has side effects; every surgery risks complications.
Unintended consequences are typically thought of as negative, but they need not be. Freakonomics author Steven Levitt and a colleague proposed, controversially, that the drop in crime rates may be ascribed to fewer children growing up unwanted after the Supreme Court's Roe v. Wade ruling in 1973. That outcome could not have been envisioned by the activists who fought for abortion rights.
Then there is, if you will, the mother of all unintended consequences: the invasion of Iraq. Before the war, Saddam Hussein served as a regional counterweight to Iran. The U.S. invasion left Iraq weak and in chaos. Now there's no muscular neighbor to check Iran's ambitions, nuclear or otherwise. The war also created a breeding ground for jihadists plus a nasty refugee crisis.
Surprise! Solving one problem (toppling a dangerous dictator) brought on several new ones. But there might have been far fewer "known unknowns" if Mr. Rumsfeld and others had not ignored the vast amount of planning - and, yes, anticipation of consequences - that was done before the war, especially by the State Department. They thought they knew better.
Unintended consequences are the way of the world; they don't need willful ignorance to help them achieve results. But help, it seems, is always in the offing.