Authors:

The more physical the activity, the less the difficulties will be. The more the activity becomes intellectual and turns into motives which exercise a determining influence on the commander's will, the more the difficulties will increase.

Carl von Clausewitz, Michael Howard, Peter Paret (1989). “On War”, p.140, Princeton University Press
The more physical the activity, the less the difficulties will be. The more the activity becomes intellectual and turns into motives which exercise a determining influence on the commander's will, the more the