"One cannot walk into the same river twice" is a famous saying of Heraclitus, an ancient Greek materialist philosopher. Lenin called him "one of the founders of dialectics". This famous saying means that the water in the river is constantly flowing. This time you stepped into the river and the water ran away. The next time you step into this river, it will flow with new water. Rivers are constantly flowing, so you can't step into the same river. Obviously, this famous saying has its own characteristics. Heraclitus advocated "the movement of all things" and "the flow of all things", which made him an outstanding representative of the "mobile school" with simple dialectical thought at that time.