Don't you know life is like a military campaign? One must serve on watch, another in reconnaissance, another on the front line... So it is for us —each person's life is a kind of battle, and a long and varied one too. You must keep watch like a soldier and do everything commanded... You have been stationed in a key post, not some lowly place, and not for a short time but for life.
—Epictetus, Discourses, 3.24.31-36 (resource) Ryan Holiday, The Daily Stoic