Moral Letters to Lucilius Section 23

Hoc est, quod ait Heraclitus: In idem flumen bis descendimus et non descendimus. Manet enim idem fluminis nomen, aqua transmissa est. Hoc in amne manifestius est quam in homine. Sed nos quoque non minus velox cursus praetervehit, et ideo admiror dementiam nostram, quod tantopere amamus rem fugacissimam, corpus, timemusque, ne quando moriamur, cum omne momentum mors prioris habitus sit. Vis tu non timere, ne semel fiat, quod cotidie fit!

C’est là ce qu’exprime Héraclite : « On ne se baigne pas deux fois dans le même courant. » C’est le même fleuve pour le nom : mais les flots d’hier sont bien loin. Ce changement, pour être plus sensible dans un fleuve que chez l’homme, n’en est pas moins rapide pour ce dernier ni moins entraînant ; aussi admiré-je la folie de nos si vifs attachements à la chose la plus fugitive, notre corps, et de ces frayeurs de mourir un jour, quand chaque instant de vie est la mort de l’état qui précède !

This is just what Heraclitus says: “We go down twice into the same river, and yet into a different river.” For the stream still keeps the same name, but the water has already flowed past. Of course this is much more evident in rivers than in human beings. Still, we mortals are also carried past in no less speedy a course; and this prompts me to marvel at our madness in cleaving with great affection to such a fleeting thing as the body, and in fearing lest some day we may die, when every instant means the death of our previous condition. Will you not stop fearing lest that may happen once which really happens every day?