The Importance of Being a Willing, Struggling Thing

Shopenhah: The essence of ourselves is just the same as the rest of reality. We're not special. We're just things that are trying to go in certain directions, just like the rest ofreality. So he says, we can think of gravity even as things trying to be in a different place from where they are. But my question is, what justification does he have for thinking this to be true? It comes back to his claim that space and time are necessary for individuation.