Ready Next gap understanding by whom in Succession Planning

 In the succession planning podcasts one of the distinctions of "Ready Next" rather than "Not Ready" is an understanding of the gap -- in other words, what growth needs to occur for the next move.  Am I right in presuming that it is the direct report who needs to understand this gap in themselves? They need to have self-awareness of their development needs?

I've seen situations where the growth areas for a direct report are clear to me as a supervisor, to my colleagues and even my boss, but the direct seems to struggle with accepting that these are areas that actually need to be improved upon if they want to advance their career. Would it be correct to say this situation qualifies as a "not ready" even if you've clearly articulated the development needs in performance reviews and such?