After a long day of hard work, her highness, Princess Celestia wishes for her life to change and be Somepony else, unaware that the words she recited was of a Secret Starswirl Spell, what happens next shows her something she couldn't see for the millenniams she's lived.

She finds out what pure happiness is.

The pain that I go through each and every day,
Let it be no longer,
Allow it all to drift away,
Let it be no longer,
Show me what happiness is,
Show me if I can wield it,
For long I've carried the burden of light,
Now give me the darkness."

A story to open people's eyes.