Here are several observations that have a bearing on supposed UFO sightings.
One: I was walking across campus one day when I ran into my roommate. He was staring at something and saying that he felt the way Mosses must have felt when he encountered the burning bush. He directed my gaze to a plant under a magnolia tree that had branches that spread wide out but it was clear underneath. The lone plant was one of those long ones that tapers to a point. A slight breeze caused it to sway, while nothing else around moved. There wasn't much else around. I didn't think the phenomenon was all that spectacular. It didn't compare in magnitude to a burning bush.
Two: I was watching an airplane flying by in the small town I lived in at the time. The airplane was towing one of those advertising signs. Across the street was a building. The airplane flew toward the building, got square with the building, and then I was momentarily jarred when it passed in front instead of disappearing behind. The airplane turned out to be a small radio controlled aircraft rather than the big manned airplane I'd thought it was.
Three: I was walking at night and saw a group of six circles of light that spun about in a circle, the circle getting wider and narrower as they danced. In the fog the apparitions appeared to be only ten feet away. This was an astonishing illusion, as I knew that the sky light that projected those beams was far away.
Now if I had not known about the skylight, and had been drunk, or eager for a religious or mysterious encounter, like my roommate had been. I might have thought I'd seen a UFO. And the radio controlled plane shows when something is in the air and you have no visual cues to judge scale, you might think you saw something strange when it might just be something ordinary. And it shows how easily UFO photos can be faked.
Four: I was laying semi awake on my bed in my apartment once, and saw what appeared to be a kid, dressed in a down jacket, like what had been in fashion in the 70s, this happened in the 80s. I tried to call out, "What are you doing here?" or something like that. As I did so I awoke, and the vision vanished. I did not feel scared, I did not feel a presence, I did not feel anything except a mild bemusement. In no way did I think I had seen a ghost, and I have never had that kind of dream experience again. In that apartment or elsewhere.