The Bodhisatta was once a student of religion. His teacher preached moral law to people he met, whether they wanted to hear it or not, and they never accepted it. His disciples encouraged him to preach only to those who wanted to hear his lessons, but he wouldn’t follow their advice.
The Bodhisatta wanted to convince his teacher to change his ways, so he started throwing rocks into a cave. Other disciples asked him what he was doing, but he didn’t answer; he just kept throwing stones. They told their master who came and asked the Bodhisatta why he did this. He answered that he wanted to make the world completely smooth by filling in every cavity and leveling every hill. His teacher responded that no mortal could do such a thing, and this made him realize that also nobody could make all people agree. He praised the Bodhisatta and promised to stop trying to convert everyone.
In the Lifetime of the Buddha
The teacher was an earlier birth of Sariputta, one of the Buddha’s top disciples. Sariputta tried to teach dharma to many wicked people, like hunters and fishers, hoping to convert them. Thought they listened out of respect, none ever accepted his teachings. His fellow disciples advised him to stop preaching to those who did not want to hear it, and this offended Sariputta.
The Buddha heard some disciples discussing Sariputta’s method of proselytizing and he told them this story so they knew Sariputta had done the same in the past.