Scott Atran in Aeon:
Throughout history, the most effective combatants, revolutionaries and insurgents have been ‘devoted actors’ fused together by dedication to non-negotiable ‘sacred values’ such as God, country or liberty. Military incursions nearly always plan for maximum force at the beginning to ensure victory. But if defenders resist, or are allowed to recoup, then the advantage often shifts to those with the will to fight as they increasingly harness resources against their attackers who are maxed-out in terms of what they are able, or willing, to commit: consider Napoleon and then Hitler and their onslaught against Russia, or the United States’ invasions of Iraq and Afghanistan. Throughout history, those willing to sacrifice for cause and comrades, and for their leaders, have often prevailed against more powerful forces that mainly rely on material incentives such as pay and punishment.