Prologue
Before
"What ever you do, make sure it makes your happy." ~ Unknown
Long time ago, there was a legend about ancient relics known to everyone in Equestria called the Elements of Harmony. Each Element has a name, a name that correspond with a trait of friendship.
Honesty, the pony that, despite the truth being hurtful, will say the truth, no matter how much consequences it brings.
Happiness, the pony that, even when things are bleak, will always stay positive and optimistic.
Kindness, the pony that gives out to help people even when a pony has done some things that cannot be forgiven.
Loyalty, the pony that, even when tempted by their greatest desires, will stand for their friends, and themselves.
Generosity, the pony that will give even when they do not have anything.
And Magic, the pony that believes that with all of those traits and a little of magic, friendship can form.
These are the Elements of Harmony, the ponies that had teamed up together to defeat those that oppose such things.
However...
That all changes when Loyalty and Happiness got into a fight.
The fight was verbal, as Loyalty and Happiness' values were conflicting with each other, and as the others got involved, Loyalty decided it'll be wise if they split up. Kindness went to try to reason with Loyalty while Magic and Honest tried to comfort Happiness, however, Kindness couldn't reason and Loyalty separated from the group. Several days later, the others separate from the Element of Magic, convinced that it's better off they aren't a team anymore.
These ponies then became leaders of factions that, later, divided the town of Ponyville with the exception of Happiness, whose Element of Harmony isn't present in the Faction Manifest.
Several years later, all ponies present in Equestria know that there are five factions: Abnegation, Generosity's faction, Amity, Kindness' faction, Candor, Honesty's faction, Dauntless, Loyalty's faction, and Erudite, Magic's faction. The leaders of these factions had settled on a date for the 16-year old foals to choose between the factions or their own faction from their birth. Ponyville is, and always will be, the center hub of all factions, the leaders noted, and that certain ponies could be in certain factions due to cities affected by the factions.
This has always been the day for at least 30 years, the leaders long gone with their children or successors taking their place as Faction Leader. No one hasn't revolted against this system due to being under the mercy of the leaders. There is a factionless, some of the ponies dubbed as "Happiness", due to the Element not having a Faction, the Element name being ironic to most.
This has always been the way.
It will always be the way.
But... one foal didn't like it one bit, because the foal knew, they knew that this was going against all things that the Elements of Harmony stood for, and they are going to change it, whether the leaders like it or not.