"I've come very close to death four times... I thought, 'I don't want to die not having seen them,' so I made it my mission to see them before I die."
According to a new joint interview with writers Steven Moffat and Russell T Davies, thinking of the Doctor as segmented incarnations isn't really how they approach writing the character at all. In fact, instead of the great differences between incarnations, (that fans love) to debate, Moffat and Davies seem to indicate that they never aim to write the Doctor particularly differently and that thinking of the character as a constant is the paradoxical secret to making each version feel authentic.