" Consider a nonstatistics example: Did the U.S. invasion of Iraq make America safer? There is only one intellectually honest answer: We will never know. The reason we will never know is that we do not know—and cannot know—what would have happened if the United States had not invaded Iraq. True, the United States did not find weapons of mass destruction. But it is possible that on the day after the United States did not invade Iraq Saddam Hussein could have climbed into the shower and said to himself, “I could really use a hydrogen bomb. I wonder if the North Koreans will sell me one?” After that, who knows? "

― Charles Wheelan , Naked Statistics: Stripping the Dread from the Data