To find fault, some one may say, is easy, and in every man's power; but to point out the proper course to be pursued in the present circumstances, that is the proof of a wise councellor.
τὸ μὲν οὖν ἐπιτιμᾶν ἴσως φήσαι τις ἂν ῥᾴδιον καὶ παντὸς εἶναι, τὸ δ᾿ ὑπὲρ τῶν παρόντων ὅ τι δεῖ πράττειν ἀποφαίνεσθαι, τοῦτ᾿ εἶναι συμβούλου.
Original text (Ancient Greek)
Notes from Wikiquote
Compare Plutarch, On Listening to Lectures, 40e:
τὸ μὲν γὰρ ἀντειπεῖν οὐ χαλεπὸν ἀλλὰ καὶ πάνυ ῥᾴδιον εἰρημένῳ λόγῳ· τὸ δ᾿ ἕτερον ἀνταναστῆναι βελτίονα παντάπασιν ἐργῶδες.
It is a thing of no great difficulty to raise objections against another man's oration,—nay, it is a very easy matter; but to produce a better in its place is a work extremely troublesome. (tr. W. W. Goodwin, 1871)