Consider two countries. Any two countries. Or any two provinces, regions, or towns.
Consider two people, living near and on either side of those borders.
Thought they live but several dozen kilometres apart, they will often have quite different languages, thoughts, and views on the world.
And we will call one a Countryaian, and the other a Countrybian, and we will know them vastly differently, based on that address of birth and residence. We will relate to them decidedly by and our behaviour towards will be based on what regional affiliation they have. They themselves will operate and even know each other as two vastly different people(s).
All more solid than the rock they stand on.
Yet the baby of one country is indistinguishable in its behaviour to that of any other country.