The following text is for the question below.    

    Once upon a time, there was an old snake who was too weak to hunt for frogs. Then, he had an idea to trap the frogs. He went to a pond full of frogs, and relaxed on the bank without any intention to hunt. At first the frogs ran away, but then they approached him. The frog king asked, "O Snake! Why don't you hunt us as usual?"

    The snake replied, "Last night, I bit a holy priest. He cursed me that from then on, I have to serve frogs. So, I lie here to give a ride on my back to any frog who needs service."

    Then, the king decided to take a ride. The snake rode him around the pond, and the king was very pleased. However, the next morning, when the king frog asked to ride on the snake back, he said, "I am too weak to crawl. I have not eaten for so long, and must eat something to be strong to give you a ride."

    The frog king decided that they must take turns to serve the snake; one frog each day to keep him strong. From then onwards, the snake gave ride to the frogs, and got to eat one frog every day. However, the king of frogs was too excited that he did not realize the frogs were rapidly decreasing. finally, one day, the snake also ate the king and the entire frogs in the pond were gone.

What is the main point of the story?