Being imprisoned in concrete leaves plenty of time for thought...especially in the case of the spirit of chaos. While Equestria assumes what is supposedly a normal life, Discord's prison is being cracked, little by little, and his intentions reside in the hearts of each of its inhabitants.
So here's a forewarning to those oblivious to the facts--it's all a game of balance. And that's all it ever will be.
(Letter format, oneshot.)