Once upon a time, there were three princes who wished to marry a princess. The princess wished to marry one of them, but not the other two. Her father however, was rather conservative, and did not feel she was ready to marry any of them. The King decided to put all three of them to tests that he believed none of them would be able to pass. First, he blindfolded them all, then led each in turn to his individual test.

 The King led Prince #1 to the base of a mountain where there were ten painted, wooden doors, glistening in the sun. "All but one of these doors in front of you are white," said the King. "If you can tell me within the next ten minutes, which door is black, then you may marry my daughter. You may not speak to anyone, and you may not remove your blindfold."

 The King led Prince #2 to a hillside, and pointed out across his lush green valleys to the edge of his kingdom, where ten beautiful buildings stood. "All but one of these buildings in front of you are white," the King said. "If you can tell me within the next ten minutes, which building is black, then you may marry my daughter. You may not speak to anyone, and you may not remove your blindfold."

 The King led Prince #3 to a magnificent dining table where ten places were impeccably laid out. "All but one of the napkins on this table are white," said the King. "If you can tell me within the next ten minutes, which napkin is black, then you may marry my daughter. You may not speak to anyone, and you may not remove your blindfold."

Ten minutes later, only one of the princes - the one the princess wished to marry - had succeeded at his individual test. Which one of the princes had succeeded?