Going back in time not sure I would need to change anything because changing any bit of it would have no me writing something crazy here or a happy one would become cynical
Maybe certain percentage of people go back in time changed a little here and there the whole world would have gone different way Wars did not happen at one time might happen at other time Inventions taken back to the past might disrupt the track and cause chaos
We might tell someone to escape from avalanche or earthquake at that time, but even nature changed its mind and shift the disasters to other places so future teller started to lose credit Amen time does not and could not never go back