Ok, get a load of this (spoiler alert):
Marcus Wright is a terminator hybridized to the point of having a human heart and brain. He's got a programmed mission, but still thinks he's human.
John Conner doesn't trust him. He's shocked that Skynet was able to build a machine that seems to really want to believe it's human. Unsure what to do, he starts listening to tapes his mother left him. She offers no clues as to how to deal with such a hybrid, closing with "Follow your heart, John."
After Wright saves his life, Conner agrees to let it go so it can take advantage of its terminator origin to infiltrate Skynet and free some prisoners. Conner will wait and help evacuate the prisoners. In the meantime, he follows Wright at a distance.
Big fight, lots of explosions, the usual molten metal stuff, and the good guys win, except John Conner, the leader of the resistance, is seriously wounded. He'll die if he doesn't get a heart transplant, but donors are rare in the post-apocalypse.
Ahh...but Wright, wishing to atone for the wrongs of his past human life and abandon the intent behind his cyborg reincarnation offers up his own heart.
So all this time Conner was following Wright, he was literally following his own heart (to be).
It's so brilliant I bet the writers never even thought of it!