Valor is a gift. Those having it never know for sure whether they have it till the test comes. And those having it in one test never know for sure if they will have it when the next test comes.
The fate of a battle is the result of a moment, of a thought: the hostile forces advance with various combinations, they attack each other and fight for a certain time; the critical moment arrives, a mental flash decides, and the least reserve accomplishes the object.