The water in the river is constantly flowing. When you step into the river this time, the water flows away. The next time you step into the river, new water flows in. The river keeps flowing, so you can't step into the same river. Obviously, this famous saying has a specific meaning and does not refer to the difference between this river and that river. Heraclitus advocated that "all things move" and "all things flow", which made him an outstanding representative of the "fluid school" with simple dialectical thinking at that time. This famous saying of Heraclitus shows that objective things are eternally in motion. Such a truth is changing and developing. Engels once commented: “This primitive, simple but essentially correct world view is the world view of ancient Greek philosophy, and it was clearly stated for the first time by Heraclitus: everything exists, and the same pair does not exist. , because everything is flowing, constantly changing, constantly coming into being and disappearing.” Heraclitus also believed that things are transformed into each other. Cold becomes hot, hot becomes cold, wet becomes dry, dry becomes wet. He also clearly asserted: "We go down the same river without going down. We exist but do not exist."