The goodness of the land favored the enrichment of particular individuals, and thus created faction which proved a fertile source of ruin. It also in… - Thucydides

To come to this war: despite the known disposition of the actors in a struggle to overrate its importance, and when it is over to return to their admiration of earlier events, yet an examination of the facts will show that it was much greater than the wars which preceded it.

In practice we always base our preparations against an enemy on the assumption that his plans are good; indeed, it is right to rest our hopes not on a belief in his blunders, but on the soundness of our provisions. Nor ought we to believe that there is much difference between man and man, but to think that the superiority lies with him who is reared in the severest school.

[F]or a time of public need they thought that there was no man like him. During the peace while he was at the head of affairs he ruled with prudence;
under his guidance Athens was safe, and reached the height of her greatness in his time. When the war began he showed that here too he had formed a true estimate of the Athenian power. He survived the commencement of hostilities two years and six months; and, after his death, his foresight was even better appreciated than during his life.

For he had told the Athenians that if they would be patient and would attend to their navy, and not seek to enlarge their dominion while the war was going on, nor imperil the existence of the city, they would be victorious; but they did all that he told them not to do, and in matters which seemingly had nothing to do with the war, from motives of private ambition and private interest they adopted a policy which had disastrous effects in respect both of themselves and of their allies; their measures, had they been successful, would only have brought honour and profit to individuals, and, when unsuccessful, crippled the city in the conduct of the war.

(Book 2 Chapter 65.4-7)