What I love about Princess Luna is that, while she has love and guidance to give, she is in need of these things as well. She is strong, but frail – self-possessed, but not without an irrational streak. Princess Luna is a living, trotting dichotomy. The very pride that had lead to her corruption and downfall as Nightmare Moon has since flipped inside out, and sublimated into a shame so strong, that it poses an equally dangerous threat.
Pinkie Pie has dedicated her life to making others smile because she has a constant need to chase away her own sadness. (We have seen this not only in her drastic reactions to situations where she has failed to bring good cheer, but also in the Smile song itself, where she literally pulls herself up out of a pit of sadness). I wrote more extensively on this in “The Duality of Pony.”
This dualistic nobility is equally present in Princess Luna. Her flaws are her strengths, and the reason she is so very good at helping others wrestle with their demons is that she is at constant war with her own. Her redemption arc was the first one of many that the show took on, and the one that has been the most developed since. There are always new layers to explore.
I think perhaps the most beautiful thing about Princess Luna is that the reason she is so apt at helping others – the reason she has so very much compassion – is that she herself has been to hell and back, and wants to protect all the children of the night from repeating her mistakes.