This is my thinking, too. On Instagram, we're seeing the best photos of the people who are on their one vacation of the year. Even if we ourselves post a vacation photo and it gets shared and liked, we won't think of it as one of "those" beautiful photos, because we just got lucky with that one. We remember our embarrassingly bad photos.

And on HN, comments are filled with insight backed up by decades of deep experience. But the Perl expert in one thread is unlikely to be the Russian historian in the other. There are few masters-of-all-trades (though they do exist, as if to inspire and mock us). Not to mention the majority of readers whose experience is rarely relevant enough to comment.