A thousand years ago, the Elements of Harmony began to drift apart after Discord's fall; each Bearer in turn was corrupted, and fell, until only Sunny Skies - Celestia - remained untainted. That's what should have happened - and what did.

A thousand years ago and a timeline away, however, Sunny Skies was a bit more flexible when Chrysalis Fell...and realized that maybe the Element of Generosity hadn't fallen far enough to not be followed.