How did kryptonite become associated with a person’s weakness in popular culture?

In the context of the Superman mythos, kryptonite originated as a radioactive mineral from the hero's home planet, Krypton, which emits radiation that severely weakens him.123

The term entered the popular lexicon after debuting on the radio program The Adventures of Superman in 1943. Over time, the word evolved from its specific fictional origins into a figurative expression used to describe a person’s profound weakness, failure, or susceptibility to a specific influence.421

This metaphorical usage mirrors the concept of an Achilles' heel, serving as a common synonym for a vulnerable point. By the 1960s, the term was frequently used in contexts entirely independent of the Superman character, solidifying its place in the English language as a descriptor for any singular factor that causes someone to lose their strength or composure.4231