*FEATURED 5/12/16 *
Twilight's dinner party to show Celestia Starlight's progress as a student of friendship was a disaster of epic proportions.
Okay, fine, that's being a little dramatic. The evening didn't go as planned of course, but some good things did come from it, it's not like anybody got hurt, and Twilight did her best (give her a break--she's new to this 'teaching' thing). So why did Celestia--normally poised and calm and understanding Celestia--look so angry? She acted like Twilight was inconveniencing her on purpose! No wonder the friendship princess was so frazzled.
Later that night, Celestia returns to Canterlot. And, after a lot of stubborn denial (and some interference from a certain being of chaos), she finally confides in Princess Luna the real reason she was so frustrated. Luna listens, comforts her, and then proceeds to do her duty as princess of the night by making everyone's evening a little more peaceful.
The night heals all wounds.