Thinking about Ten standing in front of that glass booth at the end of The End Of Time part two, listening to a man who has only ever treated him like family, who is the only friend he has left, who has never stopped believing in him, tell him that he isn't worth saving, to leave him to die.
Thinking about Fourteen standing on the other side of that glass barrier in The Star Beast, listening to that same man's granddaughter, one of the most important women in his many lives, the soulmate he never expected to find again, tell him that she doesn't matter, that her life isn't worth nearly so much as everyone else's.
And thinking about Fourteen sitting across a dinner table and seeing this kid, the next generation of a family that's meant so much to him, a girl who's already been through so much... and deciding to take her on adventures, to be her weird uncle, to refuse to let another generation of this family go on thinking they're not good enough.
Wilfred Mott didn't think he was worth it. Donna Noble didn't think she was worth it. But the Doctor will be damned if he lets Rose Noble grow up to think the same, to stand on the other side of a divide and tell him not to bother with saving her life.
