9I can do this for you. I can be a proper dad now
from Father's Day
The Doctor must have known that taking a 17 year old girl back in time to watch her father be hit and killed by a car would be a bad move. Also, probably a little insensitive. But he does it anyway. Like any normal girl missing her daddy, Rose can't help herself and stops those events from unfolding, bringing about a paradox that is about to end the world.
In order to undo the paradox, Pete realizes that the only thing that is going to make things better is his death. After some emotional words with his newly found, grown up daughter, he runs out into the street and is hit by a car, righting the universe again and ruining some poor innocent driver’s day. It's this, coupled with Rose' reaction and the scenes of her as a little girl being told the story of her father and the girl who sat with him as he died, that makes it a real tear-jerker.