Theory:

Taro was a young woodcutter. He lived with his aged parents in an old hut. One evening, a strong wind blew into the hut, and the father shivered. He wished for a cup of an expensive drink called saké. But Taro didn't have enough money, so he decided to work harder. The next day, when he was at his work, he discovered a waterfall whose water tasted like saké. He brought some of it to his father to drink. The father's health improved after he drank the magic saké. The story of sake spread around the village by nightfall through a lady who visited Taro in the afternoon. Everyone visited Taro's house that evening to taste the saké, and Taro's saké container became empty. When Taro went back to the waterfall the next morning, all his neighbours were there to take home the saké. But the waterfall gave only plain and cold water to them. But when Taro tasted it, it was the delicious saké. The magic waterfall gave the saké to the thoughtful son. When the Emperor of Japan heard about the incident, he rewarded him with \(20\) gold coins. He also named the waterfall after Taro. Hence, the thoughtful son was rewarded both by the waterfall and the emperor.