On Benefits Book III, V

In the same way, my Liberalis, as some things remain in our memory as soon as they are learned, while to know others it is not enough to have learned them, for our knowledge slips away from us unless it be kept up⁠—I allude to geometry and astronomy, and such other sciences as are hard to remember because of their intricacy⁠—so the greatness of some benefits prevents their being forgotten, while others, individually less, though many more in number, and bestowed at different times, pass from our minds, because, as I have stated above, we do not constantly think about them, and do not willingly recognize how much we owe to each of our benefactors.

Listen to the words of those who ask for favours.

There is not one of them who does not declare that his remembrance will be eternal, who does not vow himself your devoted servant and slave, or find, if he can, some even greater expression of humility with which to pledge himself.

After a brief space of time these same men avoid their former expressions, thinking them abject, and scarcely befitting freeborn men; afterwards they arrive at the same point to which, as I suppose, the worst and most ungrateful of men come⁠—that is, they forget.

So little does forgetfulness excuse ingratitude, that even the remembrance of a benefit may leave us ungrateful.