is something you can instill in a kid this late in his development.
In my experience with young men, if they haven't developed that characteristic by the end of HS, they aren't going to get it. It's just not them. You may be able to get more effort, more focus, more energy.... but the heart/grit thing seems to be an attribute that is either part of you from the beginning, or developed from an early age, IMHO.