I don't know if there were no previouslies or if my recording started late. If you want to know what happened in previous episodes, I guess you can go read the recaps.
Bailey stands still, looking pensive, as a thousand people rush around her in the hospital. Mere V.O.: "No one believes their life will turn out just kind of okay. We all think we're going to be great." If Meredith is suggesting that Bailey is anything less than great, I would suggest she think again. Meredith tells us that surgeons especially think they're going to be great. They expect it in fact -- hence the title of the episode. Sometimes I think the writers of this show are competing with the writers of Desperate Housewives and Heroes to see who can use narration to drive the show's theme home in the most ham-fisted fashion. In any case, based on the look on Miranda's face she's just realized that there's something wrong with her great expectations. Or that her copy of Great Expectations is overdue at the library.