Laudator Temporis Acti

N. Whatley, "On the Possibility of Reconstructing Marathon and Other Ancient Battles," Journal of Hellenic Studies 84 (1964) 119-139 (at 120-121):

Battles of all periods are difficult things to reconstruct. In battle many and different events happen simultaneously and changes are rapid. The actors are in a state of excitement and extreme nervous tension—the worst possible condition for viewing a situation with a proper sense of proportion. It is impossible for anyone to know what is happening in every part of an engagement and there is unlikely to be the occasion, even if there is the desire, for an impartial inquiry and examination of representative witnesses while the battle is recent and its memory fresh. There is the greatest difficulty in distinguishing what was foreseen from what was unforeseen, able generalship from a stroke of good luck.

It is particularly difficult to discover what was in the mind of a general. The general himself may not find it easy. No battle follows one simple plan. There are not only constant improvisations to meet new situations, but constant flukes and, above all, constant mistakes. But it is only human to forget the mistakes if they do not lead to disaster and the flukes if they lead to success. Similarly, outside opinion inevitably tends to regard what happened as having been carefully thought out and intended, which is by no means always the case.

Id. (at 125):

Only three things seem to be universally true of all armies:

(1) That a man takes up a certain amount of room and that therefore a large army, especially on a narrow road, takes up a great deal of room. (Xerxes' army, for instance: compare what I have said above about Plataea.) Henderson seems to me to leave this out of account altogether in his reconstruction of the movements before the first battle of Bedriacum. From Herodotus downwards many writers about ancient wars have treated armies on the march as if they were flags stuck in with pins on a Daily Telegraph war map.

(2) That a man takes time to move and that with a long column when the head halts the rear takes a long time to come up with it (and yet someone is always surprised if an army on the march delays at all before delivering battle).

(3) That a man has a stomach which must periodically be supplied with food.

I am almost inclined to add, though they are not of quite such universal truth:

(4) That generals make mistakes and do idiotic and irrational things, and

(5) That large bodies of troops are awkward things to handle, and when in contact with the enemy always tend to settle a fight in their own way.