doctor/bae
The basic principle of both these points is this: everything, and I mean everything, is certainly uncertain. Apart from the end of the universe itself, that is inevitable, but the bits in between -- the now, the then, not a psychic in this world or the next could give you an absolute.
That said, I know. Rather, I understand. I... well, it was in part why I could never give Rose what she deserved. I couldn't.