“Troops are not to be led to battle unless confident of success.”
Numquam ad certamen publicum produxeris militem, nisi cum eum uideris sperare uictoriam.
De Re Militari (also Epitoma Rei Militaris), Book III, "Dispositions for Action"
Kontext: An army is strengthened by labor and enervated by idleness. Troops are not to be led to battle unless confident of success. (General Maxims)