What principle emphasizes having a solid character within military units?

The principle that emphasizes having a solid character within military units is centered around the phrase "No better friend, no worse enemy." This concept highlights the importance of trust, loyalty, and character in both relationships within the military and in engagements with adversaries. A strong character is essential in fostering camaraderie and mutual respect among service members, as it lays the foundation for effective teamwork and mission success. When individuals exhibit integrity, they build bonds that enhance unit cohesion and reliability, ensuring that they can depend on one another in various situations.

The other principles, while important in their own right, focus on different aspects of military effectiveness. Brevity and clarity pertain to communication skills, essential for operational efficacy but not directly related to the character. Adaptability and innovation relate to the ability to respond effectively to changing circumstances, which does not specifically address the moral and ethical character that "No better friend, no worse enemy" encapsulates. Integrity and resilience specifically address personal attributes but do not encompass the wider relational concepts expressed in the correct answer, which integrates both friendship and adversarial interactions within a military context.