Central to Grossman’s argument is the premise that there is a natural inhibition to kill members of one’s own species. Soldiers are impacted by this inhibition. Without training and conditioning, a large percentage of them will not shoot to kill the enemy.

Grossman supports this assumption primarily with studies done by S.L.A. Marshall in World War II. Marshall found that only 15-20% of rifleman fired at the enemy. His studies were accepted by the military. However, in the 1980s and beyond, serious questions emerged about the accuracy of his findings. For example, there were no written records of the interviews with soldiers and no statistical records supporting the conclusions. Critics also question Grossman’s inference that the death toll and type (and amount) of weaponry used in the American Civil War suggest that soldiers were avoiding shooting the enemy. They do not find it conclusive. In short, this premise—so critical to Grossman’s theory—is controversial.

Based on this premise, Grossman maintains that psychological conditioning and training play critical roles in increasing the ratio of fire. With this training, killing becomes reflexive and automatic for soldiers rather than a conscious decision. However, Grossman presents several factors in his model that imply a soldier makes a decision to kill.