Assessing how well and how fiercely a military, and a nation, will defend itself is extraordinarily difficult. There are many factors to consider, including its leadership, the supplies at its disposal, the strength of the enemy and whether an opposing force is seen as an invader.

The miscalculations demonstrate that even in an age of electronic intercepts and analysis assisted by vast data collection, human relationships still matter in accurately assessing the morale of a country or military. Former intelligence officials say that is why it is critically important that the perspectives of people working directly with partner forces reach policymakers in Washington.

Had the U.S. view of Afghanistan been more realistic, efforts to evacuate Afghans who had assisted the American war effort could have begun earlier — or perhaps some of the billions of dollars put toward training Kabul’s military could have been spent in other ways.

With Ukraine, according to lawmakers on both sides of the aisle, if the United States had had a better sense of how strong and effective the Ukrainian resistance would be against a Russian invasion, it might have sent more weapons to the country sooner.