Gotcha. OKay, thank you. One last question...and maybe I'm thinking about this too hard.
Let's say a villain shows up "present day" in the show and wants to destroy the Earth. They won't win, because we've seen Earth in the future. Right? And destroying the Earth seems like a huge event that would certainly completely shift things, so I'd imagine the survival of the Earth itself in present day is set in stone. And if the Earth is set in stone, and the Doctor has a knowledge of history and time, shouldn't he already be aware of the villain that shows up to destroy everything? Shouldn't he be completely unsurprised by all of them? Like "Oh yeah...they showed up in 2009 and Bob defeated them" or whatever. Why doesn't he have this knowledge? Or would we say the villain showing up to destroy things is new in the time spectrum, therefore outside of a Time Lord's knowledge? Outside of expected history? But again, wouldn't that then mean they are on the path to change something set in stone? OR is it all right for a villain to show up and potentially attempt to change something set in stone, as the universe doesn't care if someone tries---its the fact that in the end they fail, and all is right with the world as these moments set in stone haven't altered. But again, if THIS were the case, shouldn't the Doctor already have knowledge of the event? Or is the Doctor himself the thing that is new, dropped into the mix?
My brain hurts...