Bai Juyi (772-846 CE) was an important poet and government official of the Tang Dynasty in China. He once asked a monk for the most essential Dharma instruction, and the monk replied by quoting the Buddha’s summary teaching, “Avoid harm. Do good. Purify the mind.”

Bai Juyi was not impressed, “Every child of three years knows these words. What I want to know is the most profound and fundamental teaching of the Buddha.” The monk replied, “Every child of three years knows these words, but white-haired men still fail to put them into practice.”

Source: Children and Old Men