Finally he’s (the Doctor) put in the position again where instead of giving your life for Time Lords and Daleks and great big mythological concepts that are very much offstage…it’s for Rose. It’s for that 19 year old shop girl from Planet Earth who is braver than brave and more loyal than anyone else in the universe. She is dying and he’s giving his life for her. Never mind wars. Never mind epic mythology. Never mind all that grand stand stuff. It’s absolutely personal and he’s at his most human. Right at the end he does a very human thing and gives his life.
Russel T. Davies on the Ninth Doctor - Doctor Who Confidential Series 1 Episode 13