Littlefinger's contributions to Game of Thrones's seventh season have been small but important so far. There was the dagger, there was the letter, and beyond that, he's just been sitting back in the shadows, staying out of the way. Some people have complained that he's lost his meddling ways, that he's done all he could to escape the disaster that is King's Landing and has found a safe place up north away from Cersei's chaos.
But Littlefinger isn't done yet. He has big plans, and according to a new Game of Thrones theory, the key is to let these people tear themselves apart so he can pick up the pieces.
In Littlefinger's plan, it doesn't matter much whether it's Cersei or Daenerys who wins; whichever one sits on the Iron Throne at the end will do so with heavy martial losses and a serious public relations problem. People hated Targaryens before one unleashed a Dothraki horde and burninated the countryside… and they hated Cersei before she blew up their religion and strutted around pregnant with her brother's baby, thus proving the rumors true that Joffrey and Tommen were never legitimate kings.
Once these armies have destroyed each other, Littlefinger can arrive with the North's legitimate daughter Sansa Stark and his ever growing army of loyal lords. Unfortunately, Jon has messed that up. He survived the Battle of the Bastards, has been named King of the North despite not having a legitimate claim, and wants to march to fight the White Walkers and decimate Littlefinger's army with which he planned to take the Iron Throne.
To do this, he needs the Stark children against each other so they can't consolidate power against him. If he isolates Sansa has him on her side with the Northern Lord's loyalty, he can claim the north. He's already started doing this with both Arya and Bran.
So when Bran shows up, Littlefinger tries to turn him into an asset. Bran is physically weak and seems like he might have some mental problems to boot; at first glance, he seems like he might be as easy to manipulate as Sweetrobin. That could even be a sweet shortcut for Littlefinger; instead of having to painstakingly chip away at Sansa's defenses, he could just get Bran to command Sansa to marry him. So Littlefinger gives Bran a neat present, tries to ingratiate himself, and starts working the "Hey, y'know, YOU'RE the rightful Lord of Winterfell, not that bastard brother of yours" angle. If he can get Bran to challenge Jon, either outcome is a win; even if Jon stays in power, Jon will take a massive hit to his reputation and the loyalty of his Stark-sworn bannermen. But instead, of course, Bran looks right through Littlefinger and tells him that "chaos is a ladder". And while it's plenty unsettling on the "I know about shit you said to Varys in private" level, it also implies that Bran knows exactly what Littlefinger is trying to do at Winterfell… create chaos so that he can climb the ladder.
And instead of trying to get on Arya's side, he chooses to pit her against Sansa. He knows Jon and Arya are close; he also knows Arya and Sansa never got along. He can pretty easily isolate Sansa from Jon and Arya using the letter, which he planted back in Episode Five.
In Jon's absence, he's stepped back and allowed Sansa to prove her ability as a leader, impressing the Northern Lords and gaining their loyalty. When Jon returns with a pet wight, asking them to work with Daenerys, they might choose to instead side with the less crazy, more legitimate Stark daughter.
But here's the kicker: Littlefinger might have misjudged all of them. Bran, if he chooses to take an interest in Winterfell politics, knows everything that's going on. And Arya has become a savvy assassin, who's well-versed in subterfuge of her own. If Bran can convince Arya and Sansa that Littlefinger is creating chaos to climb the Northern ladder, then his assassin sister can do what she does best.
