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.
(..) I don't know where you came from. What, you don't think we're the same? You've got the same lines on your forehead as me. Thank you for fixating on them. And you're stubborn. Snap. And sad... Not born sad. Some people are. You weren't. (..)2016 TvShow: Fleabag Title: Episode #1.6 Season: 1 Episode 6