In battle, what cannot be predicted is the enemy’s reaction; in exploration, what cannot be predicted is what is around the next bend in the river or on the other side of the hill. The planning process, therefore, is as much guesswork as it is intelligent forecasting of the physical needs of the expedition. It tends to be frustrating, because the planner carries with him a nagging sense that he is making some simple mistakes that could be easily corrected in the planning stage, but may cause a dead loss when the mistake is discovered midway through the voyage.
