It has recently become popular on HN to write "this" as if it is a complete thought. I don't understand this usage of "this". Can someone enlighten me?
"This" when used by itself means the poster agrees with a parent poster; it's an obnoxious upvote really. "This" when used with a preceding quote means that the poster agrees with the quote in particular. Such usage is more of an upvote for select part of the comment.
Not to get too meta but I've seen it a lot on Reddit and essentially someone is trying to say the thought was so completely expressed that they just need to suggest "This" as it is exactly how they feel as well.