Warning: the following contains spoilers for Game of Thrones season 8, episode 3, “The Long Night.”
In all the discussions leading up to “The Long Night,” the question of “who will kill the Night King?” was overwhelmingly considered in terms of aristocracy—i.e., who was born to do it by virtue of being the prophecized Prince(ss) that was Promised (PtwP) and/or Azor Ahai? But to quote book-Jorah, “prophecy is like a half-trained mule. It looks as though it might be useful, but the moment you trust in it, it kicks you in the head.” All us schmucks out there getting our Pepe Silvia on trying to figure out who the whole PwoP situation (and that also includes you, Melisandre) were doomed to fail, because, in the end, the Battle for the Dawn proved to be a meritocracy, and the person best trained to take out the Night King came out on top: Arya Stark.
Looking at social media in the direct aftermath of the big battle against the army of the dead, a lot of people felt like Arya’s achievement came out of nowhere—and not in a good way. But here’s the thing, dear reader: it did not come out of nowhere. Not at all.
Jon “I scream at zombie dragons” Snow turning out to be a massive red herring when it came to killing the Night King was admittedly a surprise. The whole resurrection thing in particular really seemed to point in the “ultimate hero against the battle against supernatural evil” direction, and he checked all the PtwP boxes pretty well. And Jon Snow’s plotline had crossed paths with the Night King’s more than any other character, which gave the impression that they were nemeses headed for an epic collision—at least, until the Night King turned his back on Jon Snow on the battlefield in the ultimate gesture of “you’re not even worth my time.” So yeah, there were a lot of neon signs pointing to Jon Snow being the one to stop the Night King pretty much from the moment the Night King was introduced, but misdirection is one of the most important storytelling tricks in the book, so that’s hardly something to riot over.
Once you get past prophecies and percieved foreshadowing, the simple fact of the matter is that Jon Snow has consistently had a whole lot on his plate besides preparing to kill the Night King. Look, he is an incredibly accomplished swordsman, of that there is no doubt. But ever since Jeor Mormont named him steward back in season one, Jon Snow has been forced to deal with this thing called “politics” that has required at least some of his attention at any given time ever since. He dealt with the King Beyond the Wall and the mutiny at Craster’s Keep, became Lord Commander of the Night’s Watch and then got killed by his own men (before being promptly resurrected), reclaimed Winterfell from the Boltons after Stannis’s army failed and got crowned King in the North in spite of expressing zero interest in the position. As of season 8, poor Jonny boy doesn’t even know what his actual name is anymore (Aejon?)—but he does know that his new lover is also his aunt, and that whole internal conflict is hardly helping the situation either. So, in sum, Jon’s had a lot of other stuff to distract him from prepping for the Night King, and also he’s in the middle of a major identity crisis at the moment, which is hardly conducive to peak battle performance.
While Jon dealt with a long series of complications, Arya honed her killing skills. Training with a blade has played a key role in her narrative journey since season one, but following her father’s beheading and especially in the aftermath of the Red Wedding, Arya’s plotline has revolved around killing. From Syrio Forrel, a former First Sword of Braavos, to Sandor Clegane, to surviving an internship with the most feared guild of assassins in the world—and defeating one of these assassins in single combat in pitch darkness (hint, hint), Arya might not have been preparing with the conscious goal of killing the Night King in mind, but she ended up being by far the most qualified for the task by the time push came to shove. She even previewed the fancy hand-work she used to kill him last season when she dueled Brienne of Tarth.
Since the end of the first season, Arya Stark has basically had two mottos: “anyone can be killed”—as she told Tywin goddamn Lannister to his face—and (“what do we say to the god of death?”) “not today.” Considering the wight army, and therefore its creator, the Night King, are literally death personified, as Gendry specifically described them to her just an episode prior, Arya taking out this most formidable enemy was not a baseless shock-value choice, but a well-developed twist that’s been a long time coming.