In the season seven finale of My Little Pony: Friendship Is Magic. When Starswirl the Bearded returns from Limbo along with the rest of the Pillars and the Pony Of Shadows, he does not bother listening to Starlight Glimmer at all about whether they should even attempt to reform Stygian.
But what if something in Starlight snapped that day? What if being ignored, gaslighted, and pushed around lit a fuse in Starlight. What if that confrontation in the library went VERY differently.