What is the origin of the idiom "be one's worst enemy" and when to use it?

The origin of the idiom "be one's worst enemy" is unclear, but it has been in use since at least the 19th century. It is commonly used to describe situations where someone is making choices that are detrimental to their own interests or well-being, despite knowing better. The phrase is often used as a warning or advice to encourage someone to change their behavior and avoid self-destructive patterns.