That's just something I came across on the interwebs recently and wanted to share. I thought Michelle (who reads this blog) and Jeremy might appreciate it, among others.
For those of you who don't watch Doctor Who, or at least haven't seen season 3 yet, it's referencing the Doctor's wonderfully unhelpful explanation of how time works. The episode in question, Blink, also just happens to be my favourite Who episode of all time. (Though I still have a couple seasons of Matt Smith to watch before I'm all caught up.)
The original line is clearly the writers' way of telling the fans "don't bother trying to figure out how time works in this show; you just have to trust us when we tell you the Doctor can't cross his own timeline and stuff." And of course, that's often how gender is, too. Ultimately, we kind of just have to take people's word for it that they experience it the way they do.