History of the Peloponnesian War

"You may learn this lesson by looking at our present misfortunes; for though enjoying the highest reputation of all the Greeks, we are now come [with this request] to you, though we were before accustomed to think that we had ourselves more power to grant what we have now come to sue for.

And yet we were not reduced to this either from decay of power, or from insolence on account of greater accession to it, but from failure in our plans, while reckoning on our ordinary resources;

a subject in which the same thing is alike incident to all. So that it is not right for you to suppose, that because of the present strength of your city and its accessions, fortune too will be always on your side.

They indeed are wise men who cautiously regard their good things as doubtful; (the same men would also deal with misfortunes more discreetly than others;) and who think that war does not conform itself to that measure on which men may wish to meddle with it, but will proceed as chances may lead them on. Such men, too, while they meet with fewest failures, because they are not elated by confiding in their military success, would be most inclined to bring the war to a conclusion during their prosperity.

And you, Athenians, have now an excellent opportunity of doing this with us; and of escaping hereafter, should you not be persuaded by us, and then meet with reverses, (which is very possible,) the imputation of having gained even your present advantages by mere chance; when you might have left behind you a character for power and wisdom exposed to no such hazard.