Think of all the years passed by in which you said to yourself "I'll do it tomorrow," and how the gods have again and again granted you periods of grace of which you have not availed yourself. It is time to realize that you are a member of the Universe, that you are born of Nature itself, and to know that a limit has been set to your time. Use every moment wisely, to perceive your inner refulgence, or 'twill be gone and nevermore within your reach.
Marcus AureliusKeep in mind how fast things pass by and are gone - those that are now, and those to come. Existence flows past us like a river; the "what" is in constant flux, the "why" has a thousand variations. Nothing is stable, not even what's right here. The infinity of past and future gapes before us - a chasm whose depths we cannot see.
Marcus AureliusMost of what we say and do is not essential. If you can eliminate it, you'll have more time, and more tranquillity. Ask yourself at every moment, 'Is this necessary?'
Marcus AureliusRemember how often you have postponed minding your interest, and let slip those opportunities the gods have given you. It is now high time to consider what sort of world you are part of, and from what kind of governor of it you are descended; that you have a set period assigned you to act in, and unless you improve it to brighten and compose your thoughts, it will quickly run off with you, and be lost beyond recovery.
Marcus Aurelius