Epictetus, Golden Sayings 125

Know you not that the thing is like warfare? 

One man's duty is to mount guard, another must go out to reconnoiter, a third to battle; all cannot be in one place, nor would it even be expedient. 

But you, instead of executing your Commander's orders, complain if anything harsher than usual is enjoined; not understanding to what condition you are bringing the army, so far as in you lies. 

If all were to follow your example, none would dig a trench, none would cast a rampart around the camp, none would keep watch, or expose himself to danger; but all turn out useless for the service of war. . . . 

Thus it is here also. Every life is a warfare, and that long and various. You must fulfill a soldier's duty, and obey each order at your Commander's nod.

Yes, if it be possible, divine what He would have done; for between that Command and this, there is no comparison, either in might or in excellence.