Bootstrap paradox

A bootstrap paradox was a sequence of events in which an event was among the causes of another event, which in turn is among the causes of the first-mentioned event.

The Twelfth Doctor once contemplated the paradox to an unknown audience. A bootstrap paradox was created whilst the Doctor and Clara were at the Drum, the Doctor gained the idea of using a hologram of a ghost version of himself, through Clara who had seen the ghost Doctor and told the Doctor about it. (TV: Before the Flood)