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. A common example was an individual who grew with a piece of music, then travelled back in time and introduced the song into the past, with the resultant question being: Who composed the song? (TV: Before the Flood)

Examples

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)

Joel Finch inadvertently inspired the pose of God in Michelangelo's Creation of Adam for the Sistine Chapel, after having been sent back to 1511 by a Weeping Angel. Joel studied the works of Michelangelo in the 21st century, and suggested this new pose based on his own recollections of the painting. Joel may have also invented the sandwich. (AUDIO: Fallen Angels)

It was the ArcHivist Hegelia's theory that the Isomorph Cybermen, the last remnant of the Neomorph Cyber-subspecies of 26th century Telos who were stranded in the 1980s after failing to change history by preventing the destruction of Mondas, made contact with the early CyberFaction on the dark side of the Moon. With the support and influence of the Isomorphs' cyber-technology, the CyberFaction would leave the Moon, splitting into separate subspecies that would ultimately come together and create the first of the Neomorph Cybermen on Telos. (AUDIO: The Ultimate Cybermen)

A bootstrap paradox was created while the Twelfth Doctor and Clara Oswald 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)

For that matter, the circumstances that brought the Eleventh Doctor and Clara Oswald together came about largely because of a bootstrap paradox. The Doctor sought Clara out after having met two of her "splinters", at the Dalek Asylum, (TV: Asylum of the Daleks) and in Victorian London. (TV: The Snowmen) The Doctor eventually found the original Clara and took her on as a companion in the hopes of solving the mystery of how she seemed to have lived and died in different times and places. Their travels together would ultimately lead to the event that saw the creation of Clara's "splinters", including those that the Doctor previously met, thus setting him on course to find the original Clara to begin with. (TV: The Name of the Doctor)

According to one account, the Fifth Doctor's recognition of the phrase wibbly wobbly, timey wimey, (TV: Time Crash) seemingly coined by his tenth incarnation, (TV: Blink) was as a result of hearing River Song say it during an adventure she had with that incarnation. (AUDIO: A Requiem for the Doctor) River herself learned the phrase from the Eleventh Doctor, (TV: The Wedding of River Song, The Angels Take Manhattan) and assured the Fifth Doctor that it would grow on him in time. (AUDIO: A Requiem for the Doctor)

Amy Pond named her daughter, Melody Pond, after her childhood friend Mels, unaware that Mels was her daughter, making Melody her own namesake. Additionally, Melody started going by the name River Song after learning of her future identity from the Eleventh Doctor and her parents. (TV: Let's Kill Hitler)

Iris Wildthyme and Panda created a bootstrap paradox in order to divert a potentially dangerous future involving malevolent aliens from the future. (PROSE: Iris Wildthyme and the Unholy Ghost)

The involvement of the Dalek Restoration Empire in the Kotturuh crisis owed itself to a bootstrap paradox. (PROSE: The Last Message) After the Doctor had defeated the Dalek Time Squad, (PROSE: All Flesh is Grass, AUDIO: Mutually Assured Destruction) a surviving Dalek drone transmitted a message warning others about the Doctor's actions and the temporal fluctuations. Hearing this message, the Emperor of the Restoration decided to investigate, making sure to place the drone's past self on the Time Squad when he formed it. (PROSE: The Last Message)

Another bootstrap paradox was created with the 13th doctor in the episode Spyfall: Part 2. The Doctor goes back in time to create instructions and install signs onto a plane on "How to survive a plane crash" for Ryan Sinclair (and the rest of the Fam) only after he survives the plane crash and peddles the idea to her at the end of the episode.