Ever thought if Arya and the Waif are, perhaps, one?

(Spoilers for Fight Club)

Arya is Tyler Durden and the Waif was an embodied split personality of her, a character she had made up inside the House of Black and White because she simply couldn't let go of her own identity. That means she was, unknowingly, the one who killed Lady Crane and stabbed herself as she fought her inner conflicts. Which is why at the end, Jaqen proclaimed Arya to be "no one," once she finally killed and let go of the Waif personality. This is just a silly theory.

Also, if you haven't seen Severance yet, check it out on Apple TV plus. It is currently my favorite series and the most thought-provoking sci-fi I've ever seen yet. The opening credits/title sequence is one of the most memorable ones, up there with the stunning Game of Thrones and the hilarious Peacemaker.