You can always summarize a long discussion by pressing the Summarize This Topic button under the first post (assuming you enter at the top, and if it’s a topic you’ve never seen before, that’s where you would enter).
This button only appears if the discussion has 50 or more replies by default though. It reduces the discussion to just the 10% most interacted (liked, replied, read, etc) posts. So a topic with 100 replies becomes a topic with 10 replies after pressing that button.
Note that Reddit now does this kind of summarization by default when you enter old reddit topics as an unregistered user, like so:
You can also easily filter the discussion in a long topic for any particular user by clicking or tapping on that user’s avatar and pressing Filter, then you’re only viewing one person’s posts.
