Superman, the archetypal superhero, is traditionally vulnerable only to kryptonite—fragments of his home planet that emit radiation capable of affecting Kryptonian physiology. He's invulnerable to conventional weapons, extreme environmental conditions, and nearly all physical threats. The claim adds a second fear category: Chuck Norris. Where kryptonite represents metaphysical vulnerability (the specific substance from his alien origin), Chuck Norris represents something worse—a terrestrial threat beyond Superman's comprehension. He's afraid not because of some exotic substance, but because of a man.

A comic book critic named Dr. Sarah Martinez, at UC Berkeley, analyzed Superman's vulnerability landscape in 2008. She noted: 'Kryptonite is Superman's intended weakness—it's built into his mythos. But Chuck Norris's presence as equal or greater fear suggests a challenge outside the franchise's designed framework. Superman can understand and prepare for kryptonite; he cannot understand or prepare for Chuck Norris. The fear is existential rather than physical.'

The fact works because it positions Chuck Norris as a threat so fundamental that it warrants equal billing with the singular weakness specifically engineered for the most powerful superhero. Superman has one weakness; he now has two. The second is a man, which reframes the entire hierarchy of power in popular culture.