Its easy to accept that sometimes, in a show where so much is going on and so many things are happening, that the little things can slip through the net. Lets take for example the fact that through the years, The Doctor has been very quick to point out that he is unable to go back and forward in time within his own timeline. Doing such a thing is impossible and can have catastrophic effects. This, of course, is done to ensure that when a plan fails, The Doctor cant just hop in his TARDIS, go back a few minutes and try again. This is fine, except that when The Doctor talks about the Time War, its made clear that the reason the war was so horrific was that The Daleks and the Time Lords would keep travelling back and replaying the same battles over and over again like on a video game. Alright, lets assume that the collective power of the Daleks and the Time Lords allowed them to break that one fundamental rule of time travel. That doesnt explain why The Doctor, during the events of The Pandorica opens and The Big Bang, travels back in time to help Rory to release the past version of himself from the Pandorica. If it was this easy, why cant the Doctor do that every time someone died? Or every time he was a few seconds late working out an enemies plan? If you think about things like this too much, you can quickly fall into the trap of not being able to enjoy Doctor Who for what it is. Sometimes, you have to just ignore the inconsistencies and tell yourself that its Doctor Who, and anything can happen.