"Unknown or Expired Link" - A failure in gauging user intent
And yet HackerNews, home of fiercely competing start-ups and friendly web apps, frequently throws a hissy fit with its 'unknown or expired link' issue, which ironically happens more frequently as you spend more time actually reading the site's content rather than mindlessly clicking through.
But not only does the site often fail to satisfy that request, it provides no method of recovery. The user can't refresh or go back a page and try again, as the IDs in URLs are meaningless and expire constantly. Context has been destroyed, and the only way to achieve your desired outcome is to start from the front page again and click through faster.
Why not annotate each 'more' link with the numeric page offset? Or with the ID of the last article on the page? Then if the cached listing is no longer available, you at least have a hope of recovering and presenting something useful instead.
The only logical explanation I can think of is that it's some sort of masochistic way of keeping people from wasting too much time on HackerNews.