It doesn't work RELIABLY; even Joan of Arc's "voices" eventually either broke down or started giving her bad info, and the story did not have a happy ending. Read the article on that first link I provided (Islam/prophecy).
I always wonder why psychics have to put up signs. They know you're coming. I wonder why they don't rush out into the street to tell me that they have some important information to impart to me, and to me alone...
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At college, during winter break, a group of students was doing 'research' on the paranormal, specifically on clairvoyance. They'd set up a table inviting people to take a multiple choice test. The gimmick was, the questions were not given, only the answers. After collecting test results, they'd see if anybody was able to correctly answer more than one would expect through random chance.
I walked up to their table. "I knew you were going to give me this test," I said, and then walked away...
--Boris