Philopoemen

Indeed, he would ignore the charts and diagrams for the illustration of tactical principles, and get his proofs and make his studies on the ground itself. The ways in which places slope to meet one another, and level plains come to an abrupt end, and all the vicissitudes and shapes of a phalanx when it is elongated and contracted again in the vicinity of ravines or ditches or narrow defiles, these he would investigate by himself as he wandered about, and discuss them with his companions.

For it would seem that he brought more zeal than was necessary to the study of military science, setting his affections on war as affording a most manifold basis for the practice of virtue, and despising as unsuccessful men those who left it to others.