Celestia gave her little sister a searching look. "I used too much power, Luna. I took on a responsibility that was meant to be shared. I tried to control both the sun and the moon, and after a thousand years, it left me exhausted. And the battle with Chrysalis only made things worse. I needed to rest. You know this, Luna. You know the way magic of that level must regenerate... especially since I closed the celestial void to us."