Theognis 591-594 (tr. Douglas E. Gerber):
One must endure what the gods give mortal men
and calmly bear both lots, neither too sick at heart in bad times nor suddenly rejoicing in good times, until the final outcome is seen.
τολμᾶν χρὴ τὰ διδοῦσι θεοὶ θνητοῖσι βροτοῖσιν,
ῥηϊδίως δὲ φέρειν ἀμφοτέρων τὸ λάχος,
μήτε κακοῖσιν ἀσῶντα λίην φρένα, μήτ᾿ ἀγαθοῖσιν
τερφθῇς ἐξαπίνης πρὶν τέλος ἄκρον ἰδεῖν.
Id. 657-658:
Don't be too vexed at heart in hard times or rejoice too much in good times, since it is the mark of a noble man to endure everything.
μηδὲν ἄγαν χαλεποῖσιν ἀσῶ φρένα μηδ᾿ ἀγαθοῖσιν
χαῖρ᾿, ἐπεὶ ἔστ᾿ ἀνδρὸς πάντα φέρειν ἀγαθοῦ.
Horace,
Odes 2.10.13-15 (tr. C.E. Bennett):
Hopeful in adversity, anxious in prosperity, is the heart that is well prepared for weal or woe.
sperat infestis, metuit secundis
alteram sortem bene praeparatum
pectus.