Seneca, Letters to Lucilius Letter 12

Your present opinion founded on understanding, your present conduct directed to social good, your present disposition contented with everything that happens — that is enough.

Of human life the time is a point, the substance flowing, the perception dull... The only thing that escorts a man on his way is philosophy.

Do not act as if thou wert going to live ten thousand years. Death hangs over thee. While thou livest, while it is in thy power, be good.