No, it's not that everyone on the sites have stories about ball lightning, or sleep paralysis, rather that everyone who comments with a story is reporting an ex

No, it's not that everyone on the sites have stories about ball lightning, or sleep paralysis, rather that everyone who comments with a story is reporting an experience with the subject of the article, ball lightning here, sleep paralysis apparently in another case. Those who don't have stories to tell about the phenomenon, or who have not experienced it, don't comment, there's nothing interesting or useful about saying "Yeah, ball lightning - that reminds me of the time when I didn't see any." Bear in mind there's a huge number of users on HN, and there were only around ten comments relating personal experiences with ball lightning. This is a tiny fraction of a percentage of the community, and similar statistics probably hold true for Reddit.