Earlier quoted context omitted.
> If you try to browse bigger threads here in HN or in Reddit you'll soon realize that you'll get lost. That never happens to me, especially on reddit, where threads are collapsible. How do you end up lost? > Especially when you come back to the site it's impossible to know what has changed. No it's not. There's a reddit gold feature for that.
You end up lost when you see there's a new reply on a thread you've been following (post count is 67 but yesterday it was 66) and then you go trying to find it for about five minutes. You end up re-reading about 30% of all the posts until you finally find what you were looking for. Repeat until you've read the entire thread 20 times. But that's not a bad experience compared to when you go read a threaded conversation…
And I don't understand your second paragraph; it never happens to me, but that doesn't mean it's not a problem. Could you help me understand why you find these threads unreadable? Do you make use of the "collapse thread" button?