she ran towards him and said before he could utter a word , father , you will not believe what took place . `` oh , i realized it , but it would never have worked back then . he pulled open the door , turned and walked away . when you are committed to writing hard science fiction , it means ( pardon the double negative ) you ca n't write about something you know not to be true . besides , i was on a mission that bob did not share . 