From the introduction to Vice-Admiral James B. Stockdale's Courage Under Fire: Testing Epictetus' Doctrines in the Laboratory of Human Behavior:
"[U]ndergirding my new confidence was the realization that I had found the proper philosophy for the military arts as I practiced them. The Roman Stoics coined the formula Vivere militare! - 'Life is being a soldier.' Epictetus in Discourses: 'Do you not know that life is a soldier's service? One must keep guard, another go out to reconnoitre, another take the field. If you neglect your responsibilities when some severe order is laid upon you, do you not understand to what a pitiful state you bring the army in so far as in you lies?' Enchiridion: 'Remember, you are an actor in a drama of such sort as
poor man, or a cripple, or a ruler, see that you act it well. For this is your business-to act well the given part, but to choose it belongs to Another.' 'Every one of us, slave or free, has come into this world with innate conceptions as to good and bad, noble and shameful, becoming and unbecoming, happiness and unhappiness, fitting and inappropriate.' 'If you regard yourself as a man and as a part of some whole, it is fitting for you now to be sick and now to make a voyage and run risks, and now to be in want,and on occasion to die before your time. Why, then are you vexed? Would you have someone else be sick of a fever now, someone else go on a voyage, someone else die? For it is impossible in such a body as ours, that is, in this universe that envelops us, among these fellow-creatures of ours, that such things should not happen, some to one man, some to another'."
James B. Stockdale. Courage Under Fire: Testing Epictetus's Doctrines in a Laboratory of Human Behavior (Hoover Essays) (Kindle Locations 98-108). Kindle Edition.