HBO Your biggest question after watching the season seven finale has an answer.
After a frustrating plot in Winterfell leading up to the finale, the Stark children gave the storyline a satisfying end. Sansa, Arya, and Bran play Littlefinger the way he's played everyone throughout his entire life.
In a grand scheme, it appears Littlefinger has convinced Sansa that Arya is trying to kill her so she can be Lady of Winterfell.
But in the finale, Sansa has Arya come to answer for her "crimes," only to reveal that the meeting is actually about all of Littlefinger's crimes: from murdering Lysa and Jon Arryn, to betraying Ned and Catelyn Stark.
Littlefinger says that no one was there to know that he betrayed Ned. But the Three-Eyed Raven (formerly known as Brandon Stark) describes the scene using Littlefinger's exact words: "I told you not to trust me."
Arya then slits Littlefinger's throat with his own dagger. 