Back on the subject of Knight And Day for a moment, isn't it interesting how our buddy Tom Cruise gets top billing over Cameron Diaz, when Diaz herself is actually the protagonist of the movie? Has anyone else caught onto this?
Remember that a "protagonist" is the lead character of any work of fiction with a "noble goal" – and he or she goes about trying to achieve that goal all through the narrative, though they're blocked from it at regular intervals. The plot hinges entirely on the protagonist (or should), as any decision he or she makes actually drives the story forward. At the end, no matter whether the protagonist achieves that noble goal or not, he or she has been irrevocably changed – not the same person at the wrap-up of the story as they were at the beginning.