Apophthegmata Laconica

Plutarch

Plutarch. Moralia, Vol. III. Babbitt, Frank Cole, translator. Cambridge, MA: Harvard University Press; London: William Heinemann Ltd., 1931 (printing).

Observing that his son was fighting impetuously against the Athenians, he said, Either add to your strength, or subtract from your courage.

Archidamus, the son of Agesilaus, when Philip after the battle of Chaeroneia, wrote him a somewhat haughty letter, wrote in reply, If you should measure your own shadow, you would not find that it has become any greater than before you were victorious.