When Rainbow Dash rushes into the library and asks Twilight to cure her, the new alicorn doesn't realize exactly what this is all about.
But as the situation becomes clearer, she understands that her friend isn't ill, but could need some advices and even to learn a new thing or two.
However, the more the two mares discuss Rainbow Dash's problem, the less easy it is to know which mare is learning from the other, what the lesson taught is and, in the end, if anything has been learned at all.
A little story without much ambition but multiples little subjects and the will to discuss what it means to understand something or to learn something.