* FridgeBrilliance:
** Pinkie is the best pony for Twilight to bring to the Canterlot archive, since she [[Recap/MyLittlePonyFriendshipIsMagicS1E2ElementsOfHarmony has a knack for locating useful things in a library]].
** Twilight resolves to stop worrying about the future. Unfortunately, she's still worried about the ''past'', so she goes back to deliver the message which started the whole mess.
** Why does the guard let Twilight into the library without question?
** [[{{Bookworm}} Knowing Twilight's character]], he must know that she makes frequent visits to the library all the time. She's also Celestia's trusted student and a national heroine. She's probably authorized to be in any part of the Archive she wants to.
*** It's also quite likely that it takes considerable magical skill to operate such powerful magic. Probably ''only'' someone as gifted as Twilight could do so. So not much need to keep most ponies away, even if they got their hooves on it they could never use it.
*** In "A Canterlot Wedding" its established that her big brother is captain of the guard. Its likely enough that they would recognize who she is and let her through.
*** Twilight or Spike probably sent a letter (offscreen) to Celestia explaining what happened. The princess probably told the guards to let her in on Tuesday morning to perpetuate the StableTimeLoop. This would also explain why Celestia was so amused to find her there that morning.
** Why does Twilight firmly grasp the IdiotBall at the end of the episode and go back in time to warn herself, even though she knows a message from her future self is what causes all the trouble?
*** At that point, she has gone for ''days'' without any sleep, under constant stress. Her judgment is [[JustifiedTrope understandably impaired]].
*** Her bout of insanity was preceded immediately by a blow to the head. Granted she's been prone to both SuperOCD and AmusingInjuries before, but it's likely that particular flower pot jarred something loose.
*** she's so relieved to learn that there's no catastrophe and that everything is fine, she just may not have been paying attention to the fact that she was repeating the loop.
*** She fully intended to travel back in time. If she didn't, she would have no reason to even be in the Canterlot Library. So, she ''had'' to go back in time to tell her past self about the time spells in the Library so [[TimeCrash all of reality wouldn't crash into itself.]]
*** The time loop wasn't fruitless. Cerberus was found and returned to his post, Ponyville was fixed up (possibly preventing a series of accidents like those that occurred in "[[Recap/MyLittlePonyFriendshipIsMagicS2E8TheMysteriousMareDoWell The Mysterious Mare-Do-Well]]"), and Twilight ''did'' learn a lesson that would have prevented her breakdown in "[[Recap/MyLittlePonyFriendshipIsMagicS2E3LessonZero Lesson Zero]]". Twilight would never have accomplished these things if she didn't go back to warn herself.
** Fluttershy can easily tame Cerberus because he ''is'' already tame! He's the guardian against the horrors of Tartarus. Guard dogs are tame creatures. (Can't be often he gets to play fetch and get tickled. Or is there somepony who takes care of him?) While he does scare the ponies at the beginning, the clear problem is that he has left Tartarus unguarded, not that he himself is that dangerous (though guard dogs can be mean if provoked, of course).
* FridgeHorror: Yes, somewhere in Equestria is a door to Tartarus that holds ancient horrors, fortunately we got Cerberus to keep evil in line.
** [[FromBadToWorse It got worse.]] [[spoiler:[[KnightOfCerebus A lot worse.]] [[Recap/MyLittlePonyFriendshipIsMagicS4E25TwilightsKingdomPart1 Something]] [[Recap/MyLittlePonyFriendshipIsMagicS4E26TwilightsKingdomPart2 escaped.]]]]
* FridgeLogic: No, seriously, where ''did'' that flower pot that fell on Twilight's head come from?[[Recap/MyLittlePonyFriendshipIsMagicS1E15FeelingPinkieKeen Derpy dropped it.]]
** How exactly was trimming Pinkie Pie's mane supposed to prevent a disaster? Trimming it helps her see better. ''[[FridgeBrilliance She found that time travel spell later on.]]''
*** Also, it was done by Rarity... to prevent a FASHION disaster.