one cannot step into the same river twice.
things change so fast that, by the time your foot hits the river bed, it’s a different river than the one it was.
Things do change, constantly. Atom by atom. Fast. And our feet, and our language, are slow. We can’t keep up.
One might well infer that nothing—be it a river or anything else—remains the same thing from moment to moment—and that our speech is like news that is out of date as soon as it appears.