This question has been asked for decades already, and still we collectively don't seem to have any real answers that help instruct us as to whatever "reality" may constitute serious, tangible data on UFOs.
Way back in 1955, Edward Ruppelt, the first director of the USAF's Project Bluebook, wrote that, "I wouldn't want to hazard a guess as to what the final outcome of the UFO investigation will be, but I am sure that within a few years there will be a proven answer."
I often wonder if Ruppelt would ever have foreseen that well after the turn of the next century, we would still be awaiting that final "proven answer" that he anticipated.
At the very least, we might say that, based on what anecdotal evidence has been collected in UFO witness testimony since the end of World War II, there appear to have been varieties of unusual aircraft seen in our skies for decades now. Their origin, however, remains a matter of conjecture, due to the lack of physical evidence to support the range of theories that have been proposed in this regard.
Hence, with little more than decades of witness testimony, and the occasional (though scant) physical evidence that turns up rarely, perhaps one of the most important questions that should be asked is, "how useful is the anecdotal evidence at our disposal?" ...read more>>>....
