And on that thought, I have a lot to say about the theme of identity throughout the Discworld in general. In every book, even the earlier, less dark ones, there’s a constant theme of being true to yourself and doing what you think is right, no matter what other people tell you, no matter what the world throws at you, no matter how life tries to wear you down.
It might be Rincewind just knowing he’s a wizard. It might be Granny Weatherwax standing in a world of mirrors and thinking it’s a trick question when she’s asked to identify which one is real, because obviously it’s her. It might be Vimes knowing he won’t let good men die even if history says that’s what happens, because it can never be what Sam Vimes says happens.
But the lesson is always the same: whoever you are inside, whatever you believe yourself to be, that is you, and nobody gets to steal that from you. Words in the heart cannot be taken.