I've seen a bunch of stories in the last couple of weeks that boil down to this quasi-plot:
Someone encounters some magical or otherwise apparently impossible phenomenon. In the end, it turns out that it's real! ~OMG, who could possibly have seen that coming?~
I mean, y'know, who other than anyone who's ever read any sf or heard a ghost story.
It's possible that I'm being oversensitive to this due to sheer volume. I read about a hundred stories last week, 60 of them over the weekend, so even if only a small percentage of them fit this mold, I'm getting a more concentrated dose of this kind of thing than usual.
But still. If for some reason you're tempted to write a story like this, just go do something else until the temptation passes.
As soon as something weird or unusual or paranormal-seeming happens in an sf story, as soon as a character even mentions some mysterious event or creature or device or occurrence, every reader who's ever read an sf story before will immediately expect the whatever it is to turn out to be real. That's one of the oldest and strongest conventions of the genre.
So don't expect the realness to be a surprise to the reader. And don't make it the point of your story.
(Somehow I seem to have left this off of our Stories We've Seen Too Often list, though there are a couple of somewhat similar items here and there. I'll add it soon.)
Of course I have to also note: don't try to subvert this genre convention by some variant. For example: ~Gasp! I, the reader, assumed it was real, but it's not real after all!~ also doesn't make a good story in and of itself.
I know I'm preaching to the choir. Really just blowing off steam.
P.S.: Entirely unrelatedly, something else I've been seeing a lot of lately is stories that unintentionally jump back and forth between past and present tense.
P.P.S.: Also unrelatedly, after a couple weeks of getting about 90 stories a week, this week we've had a sudden uptick: if the current volume continues, we'll get about 125 submissions this week, which will be in the top five highest-volume weeks ever. I wonder what happened. I sure hope it's temporary, whatever it is.