John's arc is this slow, painful rebuild of his entire identity after the war. He comes back a ghost. He's got the psychosomatic limp, the tremor, the therapist telling him he's damaged goods. Then Sherlock blasts into his life and offers him danger and purpose, but also this impossible standard to live up to. The central conflict isn't just about missing the war; it's about whether he can be extraordinary outside of it. He's constantly torn between being the stable, moral anchor and craving the adrenaline that makes him feel alive again. That's why the Mary Morstan storyline hits so hard. He finally chooses normalcy, a home, a family—the life he thought he wanted. And it blows up in his face spectacularly. His loyalty to Sherlock wars with his love for Mary, and his own sense of being a good man is shattered when he learns she's not who she seemed. In the end, his conflict is about integration. Can the soldier, the doctor, and the blogger coexist? The resolution isn't about choosing one life over the other, but learning that all those parts of him are valid, even when they're messy.
I always go back to that scene in 'The Lying Detective,' where he's beating Sherlock on the floor, screaming that he's not a good man. That's the raw core of it. He's spent years believing Sherlock's chaos needed his stability, only to confront the chaos within himself.