Here's an explanation Paul Graham posted ~6 years ago: <a href="https://news.ycombinator.com/item?id=17705" rel="nofollow">https://news.ycombinator.com/item?id=17705</a><p>The short of it is that HN uses closures stored server-side to maintain state in various places throughout the site, and purges old closures regularly. As usage has gone up, what counts as an "old" closure is now probably unreasonably short. Restarting HN also invalidates all existing closures.
If you wait too long (1 min < wait time < 10 mins, I think), the link will 'expire'. Some other sites like hckrnews.com (for articles that made the front page(s)) and hnflood and others perhaps (for /newest) address this if you are sick and twisted and like to go back into history into the raw submission feed.
The 'more' link is not what pisses me off. What really sucks is when you go to submit a thoughtful reply and you get hit with a bullshit expired event upon submission. Then you need to click 'back' open new window, and paste a fresh submission. I assume those who post long responses do so by firing up a text editor then pasting the response.<p>You would think this site would work flawlessly. Perhaps HN feels you shouldn't be on here unless you know the pitfalls. HN doesn't seem to respect the community. Would PG return to a site with such a shitty user experience? Absolutely not. I guess YC subscribes to "do as we say, not as we do..." when mentoring batches.