This reminds me of a story that I unfortunately forget the citation of: The military wanted to conduct an experiment to see if urban or rural recruits would ha

This reminds me of a story that I unfortunately forget the citation of: The military wanted to conduct an experiment to see if urban or rural recruits would have an easier time matriculating. They felt the hypothesis was obvious: rural recruits would be more “rugged” and handle extreme environments better. The experiment showed the opposite—urban recruits were matriculating better. Suddenly the conclusion was “obvious” as well: urban recruits were more accustomed to rigid lifestyles and could handle the orders barked at them. The lesson is that if two opposite results could be “obvious” then neither are. Observational studies can very easily fall into this trap.