"Imagine that the whole earth was covered with water, and that a man were to throw a yoke with a hole in it into the water. Blown by the wind, that yoke would drift north, south, east and west. Now suppose that once in a hundred years a blind turtle were to rise to the surface. What would be the chances of that turtle putting his head through the hole in the yoke as he rose to the surface once in a hundred years?"
"It would be very unlikely, Lord."
"Well, it is just as unlikely that one will be born as a human being. It is just as unlikely that a Tathagata, a Noble One, a fully enlightened Buddha should appear in the world. And it is just as unlikely that the Dhamma and discipline of the Tathagata should be proclaimed. But now you have been born as a human being, a Tathagata has appeared and the Dhamma has been proclaimed. Therefore, strive to realize the Four Noble Truths." (S.V,456)