This Is Exactly Why Sansa Makes Her Final Decision About Littlefinger

After marrying Lysa, playing on her lifelong affection for him, Littlefinger sends her tumbling out of the Moon Door. He does so to gain power in the Vale, though Baelish claims it was to protect Sansa from Lysa's jealous rage — which was probably also a factor, because let's be honest, Lysa was off her rocker. But the bigger reason was so Baelish could wield the power of the Vale as Lysa's widower.