It is only one who is thoroughly acquainted with the evils of war that
can thoroughly understand the profitable way of carrying it on.
That is, with rapidity. Only one who knows the disastrous effects
of a long war can realise the supreme importance of rapidity in
bringing it to a close. Only two commentators seem to favour this
interpretation, but it fits well into the logic of the context,
whereas the rendering, “He who does not know the evils of war
cannot appreciate its benefits,” is distinctly pointless.