The events of war are hard to predict.
Thuc. 2.11.4 (the speaker is the Spartan king Archidamus)
…
If anyone is surprised that I have written so often about working with divine favour, I can assure him he will be less surprised, if he is going to be often in peril, and if he will consider that in time of war enemies plot against each other, but they seldom know what will come of their plots. Therefore, you could not find anybody else who can give counsel in these sorts of cases except the gods. They know all things, and warn whomever they want through sacrifices, omens, voices, and dreams. And one may assume that they prefer to counsel those who do not only ask what they should do in the hour of need, but also in prosperous situations honour them at the best of their power.
Xen. Hipp. 9.8–9, see also Thuc. 1.78
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So, human knowledge does not know how to choose for the best more than if one would decide what to do by lot. But the gods, my son, being eternal know everything: past events, present ones, and what will come from each of these things, and among the men who consult them, they reveal to those towards whom they are propitious what they should and should not do. But that they do not give advice to everybody, this is hardly surprising: since nothing compels them to care if they are unwilling.
Xen. Cyr. 1.6.46
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