Starswirl – Magic
Discord – Laughter
Crysilis – Honesty
Sombra – Generosity
Luna – Kindness
Celestia – Loyalty

These were the original elements of Harmony.
Starswirl messed up and caused all of his "colleagues" to turn into something different.

Starswirl spent the last of his days trying to fix his mistake, but was only able to get Luna and Celestia back to normal and was able to pass the elements on to them.

Luna and Celestia were then given the task to seal away their "friends". Discord was turned to stone and Sombra was sealed away, Crysilis was no where to be found and then finally Luna turned into Nightmare Moon, proving that Starswirl's spell for her failed. Celestia then used the elements to seal her sister away and was then disconnected with the elements because the Harmony was no longer there.

Celestia had no knowledge nor the power to continue Starswirl's work so she was forced to wait until a true successor came up, in order for her to do this, she accepted every and any "gifted" unicorn that crossed her path, searching for the one with Starswirl's 'spark'.

Starswirl was the first ever recorded case of forever alone.