Moral Letters to Lucilius Section 9

Nescio quomodo magis vana perturbant. Vera enim modum suum habent; quicquid ex incerto venit, coniecturae et paventis animi licentiae traditur. Nulli itaque tam perniciosi, tam inrevocabiles quam lymphatici metus sunt. Ceteri enim sine ratione, hi sine mente sunt.

Je ne sais comment le chimérique alarme toujours davantage : c’est que le vrai a sa mesure, et que l’incertain avenir reste livré aux conjectures et aux hyperboles de la peur. Aussi n’est-il rien de si désastreux, de si irrémédiable que les terreurs paniques : les autres ôtent la réflexion, celles-ci, jusqu’à la pensée.

And somehow or other it is the idle report that disturbs us most. For truth has its own definite boundaries, but that which arises from uncertainty is delivered over to guesswork and the irresponsible license of a frightened mind. That is why no fear is so ruinous and so uncontrollable as panic fear. For other fears are groundless, but this fear is witless.