From the Letters to Lucilius — Lucius Annaeus Seneca

Do this, my dear Lucilius: claim yourself for yourself. Gather and guard the time that until now was being taken from you, or stolen, or simply slipping away. Persuade yourself that what I write is true: some of our time is torn from us, some is quietly withdrawn, and some merely drains off. The most shameful loss is the one that comes through carelessness. Look closely and you will see that the greater part of life is spent doing wrong, a great part doing nothing, and nearly the whole of it doing what is beside the point. While we put off living, life rushes by. Nothing is ours, Lucilius; only time is ours.