I knew there was a scientific explanation for this.
The Inverse Ninja Law is a similar phenomenon that occurs frequently in martial arts movies, and role playing games. It is also sometimes called the Anime Ninja Effect or the Rule of One.
The Inverse Ninja Law states that the effectiveness of a group of ninja is inversely proportional to the number of ninja in the group. While a single enemy ninja is often portrayed as a significant threat to the protagonists, a large group of ninja is significantly less of a threat, and as such is easily defeated. This is sometimes applicable to other close combat–oriented minions as well.
Accordingly, effectiveness, e, should be computable given the number of ninja, n, and some as-yet-undetermined proportionality constant, k, as follows:
The Stormtrooper effect, also called Stormtrooper syndrome, is a cliché phenomenon in works of fiction where minor characters (cannon fodder) are unrealistically ineffective in combat against more important characters (almost always the protagonists "equipped" with character shields). The name originated with the armed Imperial Stormtroopers in the original Star Wars trilogy, who, despite their considerable advantages of close range, overwhelming numbers, professional military training, full armor, military-grade firepower, and noticeable combat effectiveness against non-speaking characters, were incapable of seriously harming the protagonists. The effect is generally employed either to increase the dramatic tension of an action scene or to accentuate the heroes' fighting prowess.
Via Cynical-C Blog