Pulled this:

• Also in Discworld: Princess Esmerelda Margaret Note Spelling. This unusual name was the result of her mother Magrat Garlick's attempt to correct a mistake made by her own mother, who had intended for Magrat to be named "Margaret" but was unable to spell the name properly when she wrote it down for the priest. In an effort to ensure the proper naming of her child, Magrat appended "Note Spelling" in the note she passed to the priest. This back-fired when he read out the complete sentence, but the deed had been done and by their culture or law could not be changed.

Because there isn't actually a prophecy involved.

Removed:

• The other version of this myth involves Oedipus becoming an athlete, and a thrown discus killing his father, who was watching, by pure coincidence (another myth has another ancient Greek hero, Perseus, doing this to his grandfather, whom he was prophesied to kill).

Wikipedia mentions no such version of the myth; as the second part says, it was actually Perseus. (And in either case, this has nothing to do with this trope.)