Lesson Zero has become quite the iconic episode in the brony fandom.  We get some Fantastic interactions between the Mane Six.  We get a new setup to the series by allowing others besides Twilight to send letters to Princess Celestia.  And of course we have the classic scenes with Twilight losing herself to a mental break.  It was one of the first episodes I saw in the series, and it still remains one of the most memorable.

DRWolf Narrator by DavionX:
http://davionx.deviantart.com/art/DrWolf-Narrator-377863090

All other Characters and Images belong to Hasbro.