"I didn't listen. I didn't understand. I didn't try. And I thought through it, again and again, what if I did? Would that have changed anything? My life is marked with a long line of failures."

Celestia has a personal talk with Twilight. About her disappointment in herself, of failing ponies (and creatures) she met and those who were also part of her life.

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A lot of this based around headcanons and other stories in my AU. Some of them need a quick explanation:

Gaius, the ancient dragon lord: There's a longer story about this that I have written (HERE). Celestia was confident ponies way of living, sharing kindness and helping each other, would benefit the dragons too. Gaius trusted his friend, and taking her advice started to show kindness to his fellow dragons. Which led him to be overthrown by Scales and exiled from the dragon community. He blamed Celestia of him becoming 'weak'.

Radiant Hope: After Sombra's banishment and the disappearance of the Crystal Empire, she became Celestia's personal student. Shortly later Radiant started to question whether or not it was the right thing to do and if there wasn't a way to save Sombra and the Empire. Celestia many times assured her it was the only way and Sombra was a loss cause. Radiant hated that, because she knew the stallion since she was a foal. And she hated herself for betraying him. She left her mentor's side to find a way to save Sombra and bring the Empire back. That's when she was spirited away by the Umbrums.

Potion Nova (and Cosmic Prism): Similar to Gaius, her story was explored in an older drawing (HERE). In short, Potion Nova was the one behind the love potion. She may build a bit of an ego and got cocky, thinking her potions can solve everything, which led to chaos and her exiling herself into another world. Cosmic Prism was the victim of said love potion. She lived a relatively normal life after the incident, but with Potion gone, lost a dear friend.

Princess Luna: Alone and unloved, that's how Luna felt. Just a secondary thought, leaving in her sister's shadow. She wanted the Moon, the night and stars to be in the front sometimes. But everytime she suggested to make some day where the night just a bit longer Celestia refused. Many feuds happened between the two sisters, which led to Luna starting to hate her sister. And this hatred one day turned her into Nightmare Moon. Thinking there's no other option, Celestia banished her sister and locked her away into the Moon.

Tempest Shadow: Young Tempest as a last result reached out to Celestia hoping she can fix her horn something no other powerful unicorns couldn do. However, Celestia said no. Unknown wether or not because she couldn't do what Tempest requested or because she simply didn't want to. Tempest didn't accept the first one as possibility. How can someone be so powerful, but can't do something like this? This may were the last straw that pushed Tempest to turn her back on pony kind. Later outside of Equestria, she started to work for the Storm King, because he promised her what Celestia wouldn't even try. Help her.

Sunset Shimmer: She did great in her studies and was trying her hardest. Celestia still not allowed her to feel equal to her, despite the fact she transformed many of her past students into alicorns and crowned them as princesses. She made many requests and pleads, but Celestia wouldn't listen, stating she is not ready. After trying to take her destiny into her hooves and got sent away by Celestia, she escaped into another world.

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Additional notes:

1. Originally this was just about Celestia and her students, and the times she may failed them as a mentor. And that kinda evolved into something a bit more.

2. I felt like there was more to why Tempest turned her back on ponies and work for the Storm King than just what her friends done to her. It sounded logical that first she tried to get help from ponies and either they couldn't help or refused.

3. Tempest while not clearly seen here, she was an older teen at the time.

4. Currently, I think magic can be used for healing (seeing as Radiant Hope's talent is being a powerful healer) , but it has limitations. Growing back body parts is one of them. However, Celestia does have powers and spells that are unknown to other ponies. So for now it's unknown if she could really help Tempest. And if she really could why didn't she.

5. As we saw in the show, Luna took over as Nightmare Moon for like half a day maybe. For me with that name and how ponies feared her, when she returned, I think there was more, and maybe already did awful things before she turned.

So she instead of helping ponies with their nightmares she gives them even worse one, hoping they would rather stay awake during night and than let them sleep during the day (hence the Nightmare Moon name). She also hoped Celestia didn't find out, but she did. They have got into their worst argument yet and the last one before Luna became Nightmare Moon.

6. Celestia had multiple students in the past who was turned into alicorns. They are not around as in my AU, alicorns are naturally are not immortal, doesn't matter if they were turned into one or born naturally. Celestia and Luna are special cases.

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This was not about how Celestia is actually at fault for all the dark thing these ponies and creatures went through or the dark path they went down on. More about exploring the idea of someone who seems all powerful and without faults, and they think they need to be so, actually being just like anyone else. And that even they can think they do the right thing, but they may be wrong still. And that being alive for centuries doesn't change that.

Also, in Celestia's case, somewhat exploring the potential pridefulness she has, being the ruler of Equestria for so long and keeping it safe alone for almost more than a millennium. This something I may need to thought about more in future drawings