Steve, the word "exist" means to "stand out". In other words, if something can be seen as standing out, apart from whatever is around it (and there might be only space around it...or there might be space plus a variety of other things around it) then it is said to exist.

That covers the physically observable stuff. Then there are non-physical things like thought or emotion. They are also said to exist if they stand out from the other thoughts (or lack of thoughts) or the other emotions (or lack of emotions).

In other words, the moment something becomes noticeable in any way, it is said to exist...because it stands out.

Your story about the ball lightning matches perfectly my own approach to things. I go by direct experience, if I can. If no direct experience has occurred, then I make the best judgement I can on the probability of things, on the basis of what I've heard from other people, read in books, seen in photogrpahs, etc....

I had a couple of experiences like your ball lightning experience, but not with ball lightning...with what appeared to be some sort of unknown vehicles maneuvering in the sky. I think they probably were not "ours" (of Earthly manufacture), but I can't be 100% sure about that. I'm delighted that I got to see them, and I think they were probably alien vehicles of some kind, but again, I can't be 100% sure about that either. What I am sure about is that I saw them, that they were controlled vehicles of some kind, and that they did exist.

And I can't prove it to anyone, but that's okay. Those incidents have not caused me to found a UFO-based sect. ;-)

So we seem to have pretty much the same approach to things.