Applejack's letter is a bit longer than that...
"Dear Princess Celestia.
I wanted to share my thoughts with you.
I didn't learn anythin'!
I was right all along!
If you take your time to do things the right way, your work will speak for itself.
Sure, I could tell you I learned something about how my friends are always there to help me.
And I can count on them no matter what but truth is, I knew that already too."