The first time I listen the story is from Ajahn Brahm podcast (http://www.bswa.org), then I also found this story from his book “Opening the Door for Your Heart”.
Once upon a time there was a young emperor who ask questions to his teachers. None of them could give the young emperor good answers.
His three questions were:
1. When is the most important time?
2. Who is the most important person?
3. What is the most important thing to do?
Therefore the emperor seeks the answer by himself, wandering and experiencing life.