Last time the Vatican changed hands, there was mild interest in the Prophecy of St Malachy, a detailed but slightly cryptic catalogue of the next 112 popes produced by a 12th century Irish bishop. Many people claim that Pope John Paul II and Pope Benedict XVI fit Malachy's descriptions of popes 110 and 111 respectively, and that therefore the next pope will be the last. He will be called Peter the Roman, and he will be black.
As it happens, one of the front-runners to succeed Benedict XVI following his surprise resignation is called Peter, and there have been calls for an African pope to be elected.
Doubtless the cardinals will be aware of this prophecy, and will therefore be unable to avoid either self-consciously avoiding fulfilling the prophecy or self-consciously following it. What they cannot do is select a pope as if the prophecy didn't exist.
Thus a prophecy can influence behaviour, either positively or negatively.
For earlier commentary on this blog, see the POPE category.
Other prophets include @essene who tweets "What more sign PPL need than 2 bolts of lightening @ Vatican, after pope made resignation, to show Returned Jesus ruling from skies since 2008"