What is the origin of the idiom "feet of clay" and when to use it?

The idiom "feet of clay" originated from the biblical book of Daniel in the Old Testament, where a statue with a head of gold and feet made of a mixture of iron and clay symbolizes a powerful yet flawed kingdom. This idiom suggests that the person or thing in question has a vulnerable or fragile aspect that is not immediately apparent. It can be employed when discussing individuals, institutions, or even objects that initially seem flawless but later reveal their imperfections or shortcomings.