Polybius

But all historians, one may say without exception, and in no half-hearted manner, but making this the beginning and end of their labour, have impressed on us that the soundest education and training for a life of active politics is the study of History, and that surest and indeed the only method of learning how to bear bravely the vicissitudes of fortune, is to recall the calamities of others.

He indeed who believes that by studying isolated histories he can acquire a fairly just view of history as a whole, is, as it seems to me, much in the case of one, who, after having looked at the dissevered limbs of an animal once alive and beautiful, fancies he has been as good as an eyewitness of the creature itself in all its action and grace.

Some men give up their designs when they have almost reached the goal while others on the contrary obtain a victory by exerting at the last moment more vigorous efforts than before.

There is no witness so dreadful, no accuser so terrible as the conscience that dwells in the heart of every man.