Though depicted as nearly-invincible warriors (especially when they are the heroes of the story), ninja are often conversely depicted as disposable cannon fodder to be dispatched by the hero character, especially one who is a ninja himself. Thus, modern entertainment has shown ninja as either expendable, attacking in large numbers, or as nearly invulnerable solitary warriors (who are often unmasked in contrast). In effect of this common approach, a single/small group of protagonist ninja often easily defeat waves of incompetent enemy ninja on multiple occasions only to have far more trouble when facing a more competent lone ninja. This seemingly inconsistent portrayal is jokingly explained using the sarcastic "Inverse Ninja Law", (also called "Law of the Conservation of Ninjutsu" or the "Law of Diminishing Ninjas" or even the "Law of the Conservation of Whoopass") which states that ninja are weaker when they are in larger groups