He is not 'capable of' making those medical decisions himself. [=he cannot make the decisions by himself because he cannot think clearly, he is too sick, etc.]
I don't believe that she's 'capable of' murder. [=that she is the kind of person who could murder someone]
She is one of the most 'capable' [='skilled'] and versatile actresses in Hollywood.
(..) Woody's gone? Yeah, boy, the weasel ran away. Huh? Huh? I told you he was guilty. Who would've thought he was capable of such atrocities? Oh, Slink, I hope he's okay. Oh, a survivor. Where's the rebel base? Talk! I can see your will is strong. (..)1995 Toy Story