He's '(as) stubborn as a mule'. [=he's very/extremely stubborn]
She 'has a stubborn streak'. [=she is often stubborn]
She's wrong, but she's too 'stubborn' to admit it.
(..) - No, I know what to do. - Didn't you hit her? Didn't she fall? Didn't her baby die? Yes! I killed her child. Why are you so stubborn? Pay the blood money and end it. - I won't be forced into paying. - Why forced? Put yourself in their place. - I'm not responsible for their troubles. (..)2011 A Separation