Pre-Socratic Greek philosopher Heraclitus of Ephesus (c. 535 – c. 475 BCE), is sometimes referred to as “the Obscure” or “the Weeping Philosopher.” Characteristic epigrams are “The road up and the road down are the same road” and “The beginning and the end are the same.”
The narrator refers to another famous Heraclitean aphorism: “You can’t step into the same river” (or “You cannot step twice into the same river") -- meaning the river has changed between the first and any subsequent time you step into it (and you have, too!). Plato interpreted the remark to mean “Everything changes and nothing remains still.” One might call Heraclitus the emblematic thinker of the unbearable lightness of being.
Kundera’s narrator makes an analogy between Heraclitus’s river and Sabina’s hat. Its meaning, its import, even its very nature, changes each time she puts it on.
In the detail shown here from a 1509 painting, "The School of Athens," Raphael combined the ancient Greek philosopher and Raphael's contemporary Michelangelo (since he could have had no idea what Heraclitus really looked like) into one person.