We're Alive, Always In Flux.
So who are we, independent of our others' and our world? We haven't anything we can point to within ourselves that we can confidently say is a core essence that will Never' change. We might offer our personality, or values, an introvert, a romantic, or that we have a deep love of beauty. Still, these are descriptors of ways we behave or what motivates us. They aren't who we are.
We can go on with this effort, but we don't find anything we can nail down as "Who we are?" All the things we come up with are superficial and impermanent. We don't have anything we can point to within ourselves that we can confidently say is a core essence that will Never' change.
This idea doesn't say we don't exist. If we walked into a wall, our bodies would bump against it and we'd feel pain. Yes we exist! What it means is that we're constantly changing beings. We're always in flux. We're not permanent. We're not fixed entities.