Who is packed with paradoxes. It's similar to the Terminator franchise - they're fighting a time war so each iteration will be different as the two factions struggle against each other, influencing events.
If it makes you feel better, you can think of it in terms of diverging parallel realities that he intersects using the tardis.
Another possible similarity would be the the idea that the technological singularity of Skynet is considered inevitable in Terminator, his grave at Trenzalore could be inevitable as well, just from different circumstances yet to be shown.
If it makes you feel better, you can think of it in terms of diverging parallel realities that he intersects using the tardis.
Another possible similarity would be the the idea that the technological singularity of Skynet is considered inevitable in Terminator, his grave at Trenzalore could be inevitable as well, just from different circumstances yet to be shown.