Prodiagnōte

Βουλεύεσθε οὖν βραδέως ὡς οὐ περὶ βραχέων, καὶ μὴ ἀλλοτρίαις γνώμαις καὶ ἐγκλήμασι πεισθέντες οἰκεῖον πόνον πρόσθησθε. τοῦ δὲ πολέμου τὸν παράλογον ὅσος ἐστί, πρὶν ἐν αὐτῷ γενέσθαι προδιάγνωτε· μηκυνόμενος γὰρ φιλεῖ ἐς τύχας τὰ πολλὰ περιίστασθαι, ὧν ἴσον τε ἀπέχομεν καὶ ὁποτέρως ἔσται ἐν ἀδήλῳ κινδυνεύεται.
(Thucydides, Hist. 1.78.1-2)

Be slow, then, in reaching a decision: these are matters of great importance. And do not let other people’s opinions and complaints persuade you to incur troubles of your own. Give thought now to all the incalculable elements of war before you find yourselves in it. When war is prolonged it tends to become largely a matter of chance, in which we are both equally far from control and both face the danger of an uncertain outcome. And as they enter on their wars men take to action first, which should come later, and only have recourse to words when things go badly for them. (tr. Martin Hammond)