Heraclitus

According Heraclitus, the material substance (the water in the river) is constantly changing. This applies to humans too. Even if you are a human being and will always be a human being you are never the same person you were the day before. Something is always changing whether it's physically or mentally.  Even the things that appear not to be changing actually are. According to the atom theory, even though the atoms themselves are unchanged they change in other ways as they shed and gain valence electrons. Even though you cannot see an atom with the naked eye you know a change has occurred due to the fact that a type of reaction has occurred, for example, a piece of wood becoming ash. Change is an inevitable part of life.