"Doctor!" Amy Pond shouted, holding on to the silver TARDIS railing for dear life while attempting to peer over it and get a glimpse of the tweed-jacketed, bow tie-wearing man she was hollering at.
The ship was crashing, not for the first time.
"What?" The Doctor yelled back, over the blaring of alarms.
"The ship's crashing in case you hadn't noticed, DO SOMETHING!"
"Like what?" The Time Lord shouted back waggling his hands in that air, only half listening.
Maybe it was the helmic regulator, the humidity on that last planet they'd been to might have done a number on it, or maybe the brakes had worn out he hardly ever used those things, but occasionally one of them would completely blow and that would mess the old girl up. Might be the-
An especially rocking threw him to the floor. He heard a thud and the cry of "Doctor!", came again. Not so much fearful this time as truly and properly annoyed. The Doctor picked himself up, straightened his bow tie and prepared to tell Amy to hang on to something and not to worry because he had a brilliant plan.
Except just then she asked, "hasn't this thing got a manual?"
"I threw it into a supernova!"
"Why would you do that?!" Shrieked Amy in a voice that told him if the ship crashing didn't kill him, she certainly would.
The Doctor vividly remembered why. He thought back to a time about four years ago in human years, a much younger version of himself, a blonde human trapped on the other side of a blasted wall, and a Norwegian beach called Bad Wolf Bay...
He had lost her- Rose. The Doctor knew that, knew he would never see her again, but he had looked up Travel Between Parallel Worlds anyway. Sitting alone with only the TARDIS's hum for company, reading those words, "travel between parallel worlds is impossible," it had hit the Doctor: he would never see Rose again.
Then he had wrenched open the ship's doors and flung that book, containing that horrible word- impossible- out into the burning, fiery, dying sun outside.
"Because," he answered as he ran past Amy toward the console and began pressing every button he could reach. "I disagreed with it."