I'd mentioned before that, despite my respect for the achievements of Thor Hyerdahl and his expedition on the Kon-Tiki, that the quote they chose to showcase in the Kon-Tiki museum, especially as presented, was vapid and stupid beyond belief.
For that matter, despite the overwhelming leftism of the profession, you'll still find a lot of psychologists and counselors telling their patients that they need to establish boundaries. Mostly these are the ones who realize that women can be batshit-crazy BPD, and one of the overwhelming traits of BPD is an utter and total lack of personal boundaries.
I'm actually shocked that so many still discuss establishing proper boundaries between oneself and others because the very catchphrase of the left, especially the radical left, is "the personal is political" - an utter and total denial of boundaries. This of course goes on to things like "gender fluidity", and so on.
In short, they deny personal boundaries, biological boundaries, national boundaries, etc. except as, possibly, societal constructs. But in general, ideologically, and often in practice, they treat it as something that isn't real in and of itself.
But, again, boundaries do exist. Your skin, your emotional space, your personal property, your home, your family, your town, and so on. Yes, many are "social constructs" - but try to crawl into a wolverine's den and see what nature red in tooth and claw thinks of your lack of boundaries. You certainly aren't getting inside a tree very easily without tools, either.
And that whole above vs under the water thing?
Good luck getting oxygen on the wrong side of that "socially constructed" boundary or interface.
And more to the point - denial of boundaries at any scope where they exist is denial of all boundaries. Sure, you have the paradox of the sandpile - where precisely does earth, and atmosphere, etc. begin, and space end, or vice versa? - but nevertheless, in one place you clearly have planet, and in another, you have vacuum. In another location, you have a star, and each star exerts influence over its own aggregate of planets, separate from each other barring collision (aka not respecting boundaries).
Boundaries exist, at all scales. To deny them is to deny truth.