There are many jobs in which you're encouraged to expect the unexpected, but there aren't many that require that unique ability more than being an airline pilot.
Not only do pilots often have to deal with mechanical problems and unpredictable passengers, but there's also the possibility that anything else in the sky could be on a collision course with the plane at any time.
And as increasingly declassified reports of UFOs make clear, it's entirely possible for pilots to never truly find out what almost hit them.
But while we might be able to accept that we'll simply never know what some things are, it's all the more maddening when we're sure of what we're seeing, but nobody seems to be able to find it after we do.
And this bizarre lack of answers after some mysterious incidents over the last year are leaving investigators wondering if pilots have really been seeing what they think they have.