Because of the Time Lock, along with the danger of creating a paradox, the Doctor is prevented from going back in time and saving the Time Lords. The Tenth Doctor warns another character against trying to alter his own timeline as such meddling would "destroy two-thirds of the universe" and resists an offer by Krillitane Mr Finch, using the Skasis Paradigm, which would have given the Doctor the ability to reorder the universe and allowed him to stop the war. The Doctor would only change his decision and assure his race's survival after contributing to it as the Eleventh Doctor during the events of "The Day of the Doctor".