Plato, Laws 692c

ἡμῶν γιγνώσκεσθαι ταῦτα, ὅπερ εἶπον ἔμπροσθεν, νῦν μὲν γενόμενον οὐδὲν σοφόν—ἐκ γὰρ παραδείγματος ὁρᾶν γεγονότος οὐδὲν χαλεπόν—εἰ δʼ ἦν τις προορῶν τότε ταῦτα καὶ δυνάμενος μετριάσαι τὰς ἀρχὰς καὶ μίαν ἐκ τριῶν ποιῆσαι, τά τε νοηθέντα ἂν καλὰ τότε πάντα ἀπέσωσε καὶ οὐκ ἄν ποτε ὁ Περσικὸς ἐπὶ τὴν Ἑλλάδα οὐδʼ ἄλλος οὐδεὶς στόλος ἂν ὥρμησε, καταφρονήσας ὡς ὄντων ἡμῶν βραχέος ἀξίων. ἀληθῆ λέγεις.

after the occurrence, is—as I said before—no great mark of sagacity, since it is by no means difficult to draw an inference from an example in the past; but if, at the time, there had been anyone who foresaw the result and was able to moderate the ruling powers and unify them,—such a man would have preserved all the grand designs then formed, and no Persian or other armament would ever have set out against Greece, or held us in contempt as a people of small account. True.