My last girlfriend once asked what it would take for me to accept an apparently religious or supernatural experience as genuine. Being religious herself, she was unimpressed by my answer.
Over the decades, I have been startled and frightened by many strange events, but experience has taught me to consider these in the light of certain basic assumptions.
What I have seen are:
1) Normal events that I have observed poorly, or misinterpreted.
Especially at night in dark and isolated settings, the brain overcompensates for limited information by manufacturing monsters. And so I have watched UFOs that crossed the sky at alarmingly slow speeds become ordinary propeller planes. I have seen tiny bipeds in space helmets, or tall, impossibly thin humanoids, or strangely gliding "cone creatures" become ordinary deer backlit by the rising moon, or silhouetted while standing face to face with me, or cropping the grass in a park by the light of a distant lamppost that I had assumed was full size and far away, but which turned out to be not much taller than I am and very close. The brain's over-interpretation of uncertain events can keep us out of danger, but it can also give us false impressions of what is really going on.
Poor observations can also distort perception. Tricks of light and shadow, failures to gauge speeds or directions accurately, can make people suddenly vanish between one glance and the next, remove airplanes from the sky, or turn bright autumn shrubs on the pathways ahead into looming monsters of the night. The most initially-convincing UFO I have ever seen turned out to be a blimp lit up like a christmas tree, observed over a long period at sunset, when the soft light made everything magical.
2) Optical illusions, visual or auditory hallucinations, hypnopompic or hypnagogic dream states.
Especially when I am hungry, alone and isolated, or coming out of sleep, these imaginary perceptions can seem completely and often terrifyingly real. And so my bedroom has been invaded by strangers. I have heard voices call my name. I have seen statues move with menacing intent, and the planet Venus flutter like an alien spy-ship on the prowl.
3) Pranks and frauds.
What if my observations have been accurate, my perceptions unclouded by fear, fatigue, or unfamiliar circumstances? What if I saw what really seemed like a ghost or a god? Then I would most likely assume that someone was trying to fool people.
In the same way, if I had carefully observed, at length, a bizarre object in the sky, I would be less likely to think of an alien presence than the appearance of a new and perhaps military craft, but something otherwise down to Earth and human. (Unless, of course, that craft was a christmas tree blimp at sunset -- automatically alien!)
Finally, if I had eliminated these three possibilities, what I would I assume next?
4) I have gone completely crackers.
What is more likely: that Earth has been invaded, that the dead have risen from their graves, that the gods have spoken to me in person, or that I have lost my mind?
As I have mentioned, my last girlfriend was unimpressed by my standards for proof, because I seem to have none. But is that really the case?
If I were to be convinced that a religious or supernatural event was real, I would need to witness a spectacular display. After all, even a verified monster might be nothing more than a severely-deformed yet otherwise familiar animal; even a clearly-extraterrestrial ship would be a technological device, and therefore perfectly natural. Gods and ghosts remain stuck in a category of their own, and for me to believe in their existence, I would need Earth-shattering proof.
"So the sun stood still in the midst of heaven, and hasted not to go down about a whole day." That would be a start. Add a parting of the Red Sea by visible godly fingertips, and I might begin to wonder.
