On Benefits Book III, IV

Here I must do Epicurus the justice to say that he constantly complains of our ingratitude for past benefits, because we cannot bring back again, or count among our present pleasures, those good things which we have received long ago, although no pleasures can be more undeniable than those which cannot be taken from us.

Present good is not yet altogether complete, some mischance may interrupt it; the future is in suspense, and uncertain; but what is past is laid up in safety.

How can any man feel gratitude for benefits, if he skips through his whole life entirely engrossed with the present and the future?

It is remembrance that makes men grateful; and the more men hope, the less they remember.