In the official rules, this is practically required:
A good way to develop discussion is to familiarize yourself with existing threads before starting a new one. This way you avoid unnecessary overlap. If you want to expand the discussion in a completely different direction, start a new thread linked to the previous discussion.
And this should definitely be promoted more, because the safest basic assumption is that people don’t familiarize themselves with the rules or forget them. 
Just wave the flag and let’s put more focus on this from the administration’s side as well. 