What is the origin of the idiom "the pot calling the kettle black" and when to use it?

The idiom "the pot calling the kettle black" has its origins in a literal context. In the past, both pots and kettles were typically made of cast iron and were placed over an open flame for cooking. With exposure to heat, both would become blackened with soot. The phrase evolved into a metaphorical expression, suggesting hypocrisy or irony, wherein one person accuses another of a fault or behavior that they themselves are guilty of. This expression is used to highlight the inconsistency or lack of self-awareness in the accuser, likening them to the very thing they criticize.