The ideal of sustainability can’t be seen as a static goal, which represents the end of our efforts, once reached.
In practice, all complex systems need to constantly adjust their parameters to support themselves in their changing environment. And in the process, their components will change, and evolve. If from the point of view of the system as a whole we can observe this continuity, it is only possible through considerable effort and adaptation. From the point of you of the component parts that are replaced, there is no continuity, no sustainability.
This applies to physical and chemical processes, from a thermodynamic perspective, but also applies to biological evolution and the interaction of individuals and species with their changing environment.
It is up to us to recognize our power of actively intervene, so that the impact of our technologies and technological civilization doesn’t disrupt the complex interactions that we depend on, while also embracing the knowledge that we unavoidably change the world.
Building a sustainable civilization is going to become a permanent effort, to which an increasing percentage of our attention can reasonably be devoted, even if the goal is itself an ideal that can’t be reached.