"setting a line" really means having solid principles to deal with situations. it doesn't mean you have to be rigid, but it does mean you have to proactively think about what you want and what is acceptable, so you have something to fall back on when situations get complex

I think this article is a pretty good complement to ask vs. guess culture https://jeanhsu.substack.com/p/ask-vs-guess-culture

in my experience, people from ask-heavy cultures will only respond to clear lines. otherwise they will just keep pushing. if you have people in your life who are very good at recognizing soft boundaries, you don't need this skill with them, but it will be helpful for people who ignore soft boundaries.