It's universally obvious in a sense that every human culture and every human language has it (or at least I'm not aware of examples of the contrary).

And it may well be fuzzy, but it's rather telling that this fuzziness nevertheless remains confined to philosophy and metaphysics. Asharites, for example, believed that the world is recreated by God "at every moment" (and that this is what makes the notions of time, motion etc possible), so in that sense, every person is also re-created. But their societies did not derive any peculiar social customs from that belief - they still treated any person at any given moment as if they possessed stable identity over time in practice.