Copied from source:
 
Copied from his initial commission request, because he said it better than I can:  
“My idea is that while the Elements of Harmony stripped Luna of Nightmare Moons influencewhether possession, an adopted persona, or a super-powered evil side I dont know, and its really not importantthey didnt re-write her personality, meaning that she still has to deal with the emotions that led her to becoming Nightmare Moon in the first place. Living in a new time, new culture, and among new ponies would just make it harder.
 
I imagine that she spent a good many nights alone, struggling with her fear, anger, and jealousy, wondering why shes still feeling these emotions that she doesnt want, desperately trying not to fall back into the same traps all over again, paralyzed because shes afraid to go to someone for help but at the same time knows she needs it, and terrified of herself because she doesnt know which side is going to win out in the end.”
 
Re-saved as JPEG to get around the file size limitation. Original full-resolution available at source.