Once upon a time a business man goes to a distant village and offers the villagers to buy their donkeys for $10 each, so some sell their donkeys to him. Then he raises the price to $15 per donkey, and more villagers sell their donkeys. The businessman then offers $30 per donkey, so all remaining villagers sell their donkeys. At this point the businessman knowing that no more donkeys are left, he offer $50 per donkey and leaves for a weekend break.
