On the Shortness of Life: Stoic Principles for Self-Improvement

Life is divided into three periods - that which has been, that which is, that which will be. Of these the present time is short, the future is doubtful, the past is certain. For the last is the one over which Fortune has lost control, is the one which cannot be brought back under any man's power. But men who are engrossed lose this; for they have no time to look back upon the past, and even if they should have, it is not pleasant to recall something they must view with regret. They are, therefore, unwilling to direct their thoughts backward to ill-spent hours, and those whose vices become obvious if they review the past, even the vices which were disguised under some allurement of momentary pleasure, do not have the courage to revert to those hours. No one willingly turns his thought back to the past, unless all his acts have been submitted to the censorship of his conscience.