Why is it important for a nation's leaders to fully understand their adversaries and the physical and political environments in which they find themselves?

This is important so that the leaders do not get the nation into a conflict that would hurt them.

Explanation:

The important decisions that the leaders of a nation have to make are the ones that decide the future of that particular nation many times.

This is why it is important for a nation's leaders to fully understand their adversaries and the physical and political environments in which they find themselves.

The leader cannot make the mistake of getting into a conflict that will hurt their country because the ramification will be faced much later too.