I recently began to re-read Seneca's Ad Lucilium Epistulae and have been composing new notes on my reading. Here are some words from Seneca:
"Quaedam tempora eripiuntur nobis, quaedam subducuntur, quaedam effluunt. Turpissima tamen est iactura, quae per neglegentiam fit . . . Maxima pars vitae elabitur male agentibus, magna nihil agentibus, tota vita aliud agentibus. Quem mihi dabis, qui aliquod pretium tempori ponat, qui diem aesitmet, qui intellegat se cotidie mori? In hoc enim fallimur, quod motem prospicimus; magna pars eius iam praeterit. Quicquid aetatis retro est, mors tenet."
"Some moments are torn away from us, some are gently removed, others simply flow away. The most disgraceful loss of time is that which happens through carelessness . . . The greatest portion of our life passes while we are doing ill, a great part while we are doing nothing, our whole life while we are doing something else [other than what we ought]. What person will you present to me, who places any value upon his time, who reckons the value of each day, who understands that we are daily dying? For we are mistaken, when we look forward to death' the major part of death has already passed. Whatever time lies behind us, it is in death's hands."
The Stoics taught serenity, but also responsibility. One cannot simply resign oneself to doing nothing - that would not be virtuous use of our time, and thus it would not be virtuous, nor good, and thus we would not be able to enjoy serenity. Make the best possible use of time. That is the way of Virtue.