As I wrote elsewhere: "it always cheers me up and since I became a brony, I never felt extremely sad or depressive again, no matter what happened.
I used to be a very shy and often pessimist person, but watching mlp:fim made me pretty optimistic. In difficult situations Pinkie, Twi, Dashie, AJ, Rarity and Fluttershy are showing in front of my inner eye and help me find a solution or make me feel more confident. Iam really amazed what strong positive influence this show can have on the viewer."
Also it helped me to understand my friends a bit better and I think I began to appreciate them more. The lessons that mlp teaches may seem kinda obvious, but it's a very good reminder and you can learn a lot of the Ponies and the situations they get in