Practice is the source of cognition, and cognition is the active reflection of the subject on the object. The Duck Prophet of Warmth in the Spring River describes ducks playing in the water. They are the first to notice the warming of the river in early spring. The reason why ducks can predict the warming of spring river water is because they live in the water and deal with the river water every day. This poem emphasizes the importance of gaining true knowledge through practice. Only through personal practice and going deep into the inside of things can we gain a true and profound understanding of things.