7. Ending Doctor Donna
The Doctor is the man who saves everyone, and he had to save Donna. Unfortunately, that meant destroying everything she was and walking out of her life forever. He may have wanted to run about the universe for the next hundred years with her, but he couldn't and he knew it. He didn't even consider not taking the memories from Donna, because he knew that the alternative was death. Donna didn't want him to take the memoriesshe begged him not tobut she didn't fight him, or try to stop him. She didn't want to die either death, so it was on the Doctor to choose which death she would suffer. And that was the end of Donna as we knew her.