Looks like this’ll be a talks a lot story. “Here’s why I did what I did.” I’m not expecting much, but that’s up to the writer; to prove me wrong.

I wasn’t wrong, yet I really was!
A classic trope wherein protege apologizes to mentor for the mistakes of their past, but this works so well that it actually gripped me.

Grammar/Formatting—
Save for common (“Blahblah.” Soandso said.) issues, it was really spot on and I wasn’t hindered by glaring errors or plot twists/holes. It was really straight up in it's objective.
In my experience ("Blahblah," Soandso said.) is what I'm used to. A comma before the quote ends, to keep the sentence together and continuing.

Dialogue/Narration/POV—
Characters were Celestia and Sunset Shimmer. In character and on point. I’m not much of a fan of either of these ponies, yet when they interacted, I felt like I was watching an episode that we sorely need.

Worldbuilding—
Done very well! I was in the room they were in, sitting in a corner, listening and watching as they shared their experiences and stories.
The only slight issue I found, was when Sunset was describing the castle from her memory and how it was so much the same, it felt flat at times. Like, there was a redundancy within the text that wasn’t obvious, yet echoed slightly in the back of my mind when it came across.

Pacing—
Done very well, as well. Sunset and Celestia interact in a fluidic fashion and it’s totally natural, even the movements are done in such a way that it flows into the mental imagery.

Impression—
A story anyone should read if they wants their cuteness meter to be filled. This story offers some really good possibilities and muddy watered choices about why Sunset left Equestria.

Reviewer’s note:
For fans of Sunset Shimmer, this story really does offer a good backstory into Sunset that the show has yet to delve into.

Don't forget to vote and comment on the stories you read; writers appreciate it more than you know!

One pointer to offer for future reference. Our group is pretty relaxed when it comes to how you do your reviews, but the one thing that needs to be uniform are your rating tiers. Our group uses a five-rank system, which is Needs Work, Enjoyable, Recommended, Must Read, and Masterpiece. You don't have to use a numerical grading system like I do, but if you do, it needs to be roughly equal to the one I use. So far as I can tell, this story is ranked at your third tier, which would normally grade as Recommended, and therefore be worthy of being added to the recommended folder.

Other than that, nice job!