Harmony and disharmony need to remain in constant balance, as neither can exist without the other. When it's time for the bearer of disharmony to die, a new one is chosen. As Celestia passed on responsibility of the Elements of Harmony, so too did Discord inherit the Spirit of Disharmony.
It is not a quick process.
Written in one night in a feverish haze. No beta we die like men
Deep shit, but in a high way
This was a fun read!