I recently shared with my brother the fact that Wrath of Khan was at some point in the process titled The Undiscovered Country.
He said something noncommittal about how that would have been a good title too, and I said it would have been a terrible title since the quote is about the future and the movie isn't.
Then we both observed that for both Khan and Kirk it's really about the past.
And then I said, "One of them hasn't changed and the other one wishes he hadn't."
And it struck us both that Kirk and Khan are opposites on that. Khan is still the man he was fifteen years ago, filled with blinding anger at Kirk, while Kirk misses the person he was and struggles to figure out who to be now.