Indeed it seems to me that man, who is supposed to be the most cunning of all animals, is in fact the most easily duped.
For how many camps and fortresses, how many great cities have not been betrayed by this means? And though this has constantly happened in the sight of all men, yet somehow or other we always remain novices and display all the candour of youth with regard to such tricks. The reason of this is that we have not ready to hand in our memories the various disasters that have overtaken others, but while we spare no pains and expense in laying in supplies of corn and money and in constructing walls and providing missiles to guard against surprises, we all completely neglect the very easiest precaution and that which is of the greatest service at a critical moment, although we can gain this experience from study of history and inquiry while enjoying honourable repose and procuring entertainment for our minds.
(Source: Polybius, The Histories, Vol.IIΙ, Book V, Loeb Classical Library)
Research-Selection for NovoScriptorium: Anastasius Philoponus