Princess Celestia asked the element bearers to write her friendship reports. When she reads about how Twilight overcame Tirek, she is surprised and... somewhat less than pleased.

After all, as the Princess of Friendship, shouldn't she have tried to work through Tirek's issues? Shouldn't she have tried to reform him? Shouldn't she have known better than to give the villain all their power?

And then there is that one, last, thing...