I have quite limited experience with kids, but I noted something interesting several years ago when I had a light relationship with a girl who had a three year-old daughter. The daughter would take off my sunglasses and say “Not mine; yours!” and generally engage in other behavior that showed she was learning about possession. I commented such to my friend who had formally studied psychology, and he said that it was classic behavior for that age.
Yet in the adult world, note how many people are apparently not smarter than a three year-old. Yes, my experiences with skateboarding, alcoholism, and homelessness give me a biased perspective, but have you ever heard any of the following?:
A bartender say “Get out of my bar!”
A security guard demand that you leave his building.
A regular store clerk tell you to “You leave my store!”
A cop say “I don’t want to see you [doing that] on my street.”
“No problem, barkeep/rent-a-cop/Apu/pig. I just want to see a deed if you’re claiming ownership. Otherwise, why don’t I just tell you to get the fuck out of my face? You see, I actually do own that.”