"There are alternate universes? Why does no one ever tell me anything?"

"You really, really don't want anything to do with Pinkie Pie's alternate universes."

"Discord is also in tune with all alternate universe versions of himself! It's how he can see everyone talking about us right now!"

Discord groans. "That's not funny and also not even true."

"...anyway, girls, like I was saying, if you can predict the future, you can change the past, because back when the present was the future, the past was the present...predicting the future is like sending a message into the past—no, it is, if you can do one you can do the other—"

"Sorry, Twi, but that made even less sense than the last one."

"No, no, it makes sense," says Fluttershy. "She added a lot of extra words, but if you can see the future, then future-you can write you a note, right?"

"Why didn't she just say that?" mutters Applejack, mostly to herself.

"If I could do that, I could just look into the future to see what next season's fashion trends will be, and then I'd have the trendiest boutique in Equestria!" says Rarity dreamily.

"But then you'd be setting the trends," says Fluttershy, "and if you do that, where did the trends come from in the first place?"

"Didn't you hear what Princess Celestia said? There isn't just one future, and the future you see isn't necessarily the future you end up in—no, wait, it can't be, it'd be like having a spell that tells you whether another spell stabilizes, Canter's argument should apply. She'd have to be seeing some other future where the trends were set the normal way." (Not that she has any idea what this is.)

"Then how is it any different when Discord does it?"

"You should ignore that. He's just messing with you."

"Isn't he always messing with us?"

"Yes, Rainbow Dash, it is rather the entire reason for my existence. But I'm feeling nice today, so I'll give you a hint: the puzzle would be almost the same even if I didn't have some of my more, ah, unique powers."

"—anyway, Applejack, how is it different when Discord does it? Or, no, it's not that it's Discord doing it, he said it would be the same without his powers, so it isn't that he can control which future he ends up in—there must be some limits to that, by the way, he can't end up in a future he's previously seen any more than anyone else can; chaos gods aren't immune to diagonalization—"

She thinks silently for a while.

"I've got nothing."

"This is a waste of time," says Rainbow Dash. "The Princess already said he couldn't control our choices."

—can't control their choices—chaos can't—

"—that's it!!"

"No one can control which future we end up in, but we're the same in every possible future! Discord doesn't have to have seen our particular future to be able to predict what we'll choose, he just has to have seen us, because we'll make the same choice every time we're in this situation! And that's why we can't just say 'well, the Elements are either in the vault or they're not' and ignore Discord's games, because then we would have made the same choice in whatever future Discord saw, and he would have stolen the Elements!"

"That kinda sounds to me like we're letting Discord control our choices after all."

"—no, no, no, no, no," she says, still giddy with epiphany. "It's not Discord controlling our choices, it's us! Versions of us from another timeline, or another universe, or something, but I think that's sometimes how it has to be—well, it doesn't have to, you could make all of your choices at random if you wanted, but then who would trust you?—"

"He makes all of his choices at random," she says, taking off again.

Applejack grabs her tail.