It's like how they keep the TSA x-ray readers at the airport from becoming too complacent, every once in a while you have to slip a gun through the scanner and

It's like how they keep the TSA x-ray readers at the airport from becoming too complacent, every once in a while you have to slip a gun through the scanner and see if they catch it. Otherwise you're just looking for (presumably) rare events and you become numb to the never-ending stream.