Ah yes, the good old security clearance polygraph. My friend failed that one 3 times through nervousness. I believe that whole process is just partly to make you nervous and off-balance while they ask you probing questions and partly to signal that you, as an applicant, are willing to ask "how high?" when the government says jump. I did a few clearance processes when I was in the military, ultimately got a TS-SCI, but never took a polygraph; I think because I had a clean-as-a-sheet record since I joined the military a week after my 18th birthday.