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 Bad Wolf entity's existence was the result of a bootstrap paradox. Rose Tyler only looked into the heart of the TARDIS, creating the Bad Wolf, after she was motivated by seeing Bad Wolf graffiti, which she created after becoming the Bad Wolf herself. (TV: Rose, Aliens of London, The Parting of the Ways)

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)