"Right," Twilight said, nodding. "But the Elements work best with the harmony of friendship backing them up. When she wielded them alone, well, it's hard to harmonize with yourself. That's why my friends and I use them much more strongly than Celestia alone, and why we were able to cleanse Nightmare Moon, rather than locking her up. And, with Discord, they took the very embodiment of Chaos, imprisoning him in inflexible stone." 