A doctor, with many years of formal education and training, may or may not be a healer. In some cases, the way a doctor practices is the reason why a veteran drops out of treatment, never to return. But a “Doc,” someone who builds the kind of deep trust veterans had in the service with their medics—that person is a healer.

Based on more than a decade of walking with warriors, and the work of fellow authors like Karl Marlantes, Sebastian Junger, Steven Pressfield, Richard Strozzi-Heckler, Josh Mantz, and Scott Huesing,...