The Wall and the Spitfire

"But data from his own administration repeatedly show that a rising number of smuggled drugs, especially more potent ones like heroin and cocaine, are increasingly seized at legal ports of entry, which are not impacted by a wall."  -- AZ Republic, 1/8/19

We don't need a wall because we catch the most smuggled drugs at ports of entry?   This brings to mind how the British decided where to armor their Spitfire fighter planes during WWII.  Fighters need to be light to be fast and maneuverable.   When you want as little extra weight as possible, where do you add the armor.   The British put their crack operations researchers to work and gathered data on bullet holes.   When they were done and presented their data to the Royal Air Force, a young pilot shouted:  "Eureka!   Put more armor where the most bullet holes are."   The old professor leading the operations research team quietly shook his head and then spoke:  "No, young man, that is not where to put the armor.  The planes with the bullet holes all came home safely.   We need to put the armor where our data shows there aren't any bullet holes.  Where our data shows no bullet holes is where the fighters were shot that didn't come back."   Because we are catching smugglers at one place, doesn't tell us that there isn't smuggling where we're not trying hard to intercept it and, therefore, have no data, ie, bullet holes, about the incidence of smuggling in those places. 

Thank God, they didn't let "journalists" design the Spitfires.