It’s called “falling in love with your source.” I did it, my colleagues did it, intelligence professionals collectively do it, and none of us are ever the better for it. Here’s how it happens, at least from the collector level. I spent 20 years in the U.S. Army as an interrogator and strategic debriefer, with most of my second decade of service spent in and around embassies in the Middle East. My job at the embassy was to debrief walk-in sources, defectors, visa applicants of particular interest who agreed to talk to me, and anyone else of interest to the...