My own submission from a year ago [0] which is quite meager compared to most of those Show HN posts was developed in the free time I could scrounge out over a period of 3 months. I spent another month or so after that polishing a first version. Then I took a break from hobby programming for half a year to play some games that were sitting in my steam account, and now over the course of the past few months I've been developing a javascript library to sync JSON data in a P2P way, which will take another few months until it's ready to post to HN (if I ever finish it ;) ). It's not easy to find time for programming hobby projects when you have a family, a job, a life and a collection of books/games/movies to get through :)
Anyway, the way that I see it you have to do these projects for yourself, not for anyone else. You write them to scratch an itch, to see an idea blossom or wither, to enjoy the act of coding. Posting them online is the thing you do after you've done the thing you wanted to do.
I know when I originally started frequenting HN, I felt enlightened, educated, and sometimes motivated by some of the posts I saw.
Nowadays, I feel overwhelmed and discouraged from everything going on and what I seem to be missing. But I think you're dead-on -- it's all an illusion.
Yeah, I seem to get this false sense of these Show HN all being something that someone whipped up in the weekend, even though the magnitude of implies that that is very, very unlikely. It's like I think that since that they are all so easy to find, and they happen so often, the time that these seeming wizards made them is proportional to how much attention I have put on them, which is clearly erroneous. Looking at the projects they are often years old, maybe even years in the making.
I think I crossed the line of being more demotivated than inspired by those types of posts. I should cut down on this Web-thing.