I could have gone to a host of places where I haven't been, had all sorts of experiences, travelled to the most distant lands, and everything I'd have perceived, I would necessarily have drawn it from myself, for I don't go out of myself.
For Aristotle, a being, for example, an animal, is born, grows, reaches its full development, generates another, and dies etc. What does that mean? It means only that this being senses that it is not completely itself. If it were completely itself, if it were a pure form, as Aristotle says, a pure idea, if it were completely itself, it wouldn't have to change. It changes because it's looking for itself.
In Schopenhauer's theory we are wills or, rather, we are phenomena of the will in general. We will in order to will, and when we have obtained what we willed for, we necessarily will something else, because by definition we are beings who are always in movement, who consequently always will.
We see that in this belief in fate there is something that raises us up, that encourages our pride because we feel that we are in league with this superhuman force that governs everything. While we suffer its effects, we also participate in it.