Why do links expire so quick in HN?

Sometimes I spend hours on HN clicking next, next, next but it comes to a point where I "spend too much time" reading some article and when I come back and press next again then the page has expired and I've to go back to the beginning and click next a few times to get back where I was. To "prevent" this I just click next a bunch of times when I first get into HN and then go back and forward with the history arrows. Is there any "hack" I can use in my browser to prevent this? Maybe with a userscript or something?