Keep your head. Seneca, Epistles 2.13.13

Seneca advises us to have our own opinions, even when they are wrong. If you let others dictate to you against your own judgment, you lose the ability to control your emotions (especially fear). Even if you are persuaded by a belief not your own, make it yours before you dare to embrace it. That way you will not refer to others to learn how you should feel about it. The wisdom of crowds is always to be doubted, especially when history vindicates it (or appears to do so, anyway).

Ergo spem ac metum examina, et quotiens incerta erunt omnia, tibi fave: crede quod mavis. Si plures habebit sententias metus, nihilominus in hanc partem potius inclina et perturbare te desine ac subinde hoc in animo volve, maiorem partem mortalium, cum illi nec sit quicquam mali nec pro certo futurum sit, aestuare ac discurrere. Nemo enim resistit sibi, cum coepit impelli, nec timorem suum redigit ad verum; nemo dicit vanus auctor est, vanus aut finxit aut credidit. Damus nos referendis (†). Expavescimus dubia pro certis. Non servamus modum rerum. Statim in timorem venit scrupulus.

Therefore, check your fear and your hope, and whenever things become uncertain, do yourself a favor: believe what you prefer. If fear offers you more persuasive reasons than other motives, still you should maintain your course, avoiding the temptation to become anxious. Keep this thought constantly in your mind, that the greater part of mortals rages and rants even when there is no evil present, nor any guarantee that one will appear in future. No one in the panicked herd resists when he begins to be driven. No one leads his fear back to reality. No one says, "The author of this panic is an empty fool; he makes it from nothing, or inherits it from no sound reason." Instead, we give ourselves over to the herd that must be driven back. We lose our minds with dread over doubts, not certainties. We hold no fixed position in the midst of things. The least difficulty we encounter delivers us instantly to terror.

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(†) I think referendis, the reading of the MSS, makes more sense in context than the emendation proposed by Bücheler: aurae ferendos. His reading would yield something like, "We give ourselves over to be driven by the wind," changing the metaphor introduced by redigit instead of agreeing with it, as referendis does.