Upon being summoned to Canterlot, Celestia offers to show Twilight a spell that will allow them to view a world beyond anything they can imagine....a world so like their own, yet so different.
"The world we see will very likely be beyond our understanding. There is no telling what will be there or how much different this world will be from our own....Understand?"

"Of course, Princess."

To view into a world unknown, is to invite one's heart to break and bend in ways we could never fathom....by doing so, we might incite chaos and disorder into what we know.