Flying-saucer debunker Robert Sheaffer calls UFO encounters “jealous phenomena,” meaning that UFOs are finicky about letting themselves be seen. In The UFO Verdict he writes, “It is a well-known fact that UFOs are supposed to be extremely wary of showing themselves openly …. They will not … under any circumstances fly low over a crowded vacation site in broad daylight or hover conspicuously over a major city, because the photographic record they would presumably leave behind would be clear and unmistakable …. In short, one must conclude that the UFOs’ reported behavior is principally determined by an overriding concern with human thoughts and emotions.”

Similar behavior was attributed years ago to — don’t laugh — fairies. In 1920 Sir Arthur Conan Doyle, the creator of Sherlock Holmes and a sucker for tales from the unknown, proclaimed in all seriousness that fairies existed. He even published photos of them taken by a young woman, inspiring a rash of sighting reports by others. But Doyle never saw the fairies himself — like UFOs, they were a jealous phenomenon that would only reveal itself to those with the Right Stuff. It was later learned that the poses of the fairies had probably been copied from an illustration in a children’s book.

The moral of this story, of course, is that jealous phenomena almost always turn out to be illusions or hoaxes. In the case of UFOs it’s easy to see how this happens. The typical sighting occurs at night, when you can readily mistake a planet, satellite, aircraft, etc., for an alien visitor. (The planet Venus, which is quite bright, is notorious in this regard.)