In any case, the shrewd old man wanted to make the proposal "fairer" to the young lady. He said, I will put two pebbles into the bag and you pick one. Should you pick a black pebble, you are to marry me and I will extinguish your father's debt. If you pick the white pebble, you do not have to marry me, yet I will still extinguish your father's debt. If you picked neither, I shall have your father thrown into prison.
With that said, the old man picked two pebbles from the ground which is full of pebbles and put them in a bag. The young girl's sharp eyes caught the old man stuffing two black pebbles into the bag. What can she do? Expose the cheat? Or sacrifice herself? Or let her father go to jail?
What would you do?
This calls for lateral thinking over logical thinking (For more on lateral thinking, read Edward De Bono's books).
What the girl did was she reached into the bag and picked out one pebble. And dropped it onto the ground (full of pebbles) before anyone could see the colour of the one she picked.
"Oops. Clumsy me." announce the young girl apologetically.
"Never mind. The pebble left in the bag would prove which pebble I picked first", offered the girl, knowing very well, the other pebble left in the bag is surely black. And that way, "proves" the first pebble must have been white.
The old man did not dare to reveal he cheated in the first place and therefore had to extinguish the debt without a bride in return. This is how the young lady turned a seemingly hopeless situation to a most advantageous result, with a little bit of lateral thinking.
Moral of the story - a solution exists in every problem. Just take a moment to examine it from a few more angles.
(This interesting story extracted from a PPT circulating on the internet)