mightymads:
After Tarsus Jim was reclusive, and the only person who managed to get him to talk and helped him to process what happened was his paternal grandfather Tiberius. But in a year Tiberius died. That’s when Jim became self-destructive. He was searching for physical pain (bar brawls, smashing cars, etc.) to get distracted from the emotional one. His mother and brother pleaded with him to stop, had him see therapists, but such behavior would still surface from time to time. He didn’t quite trust therapists.
Then Jim enlisted in Starfleet because of Pike’s challenge. He became friends with Bones. It is known from TOS that McCoy has a degree in psychology, so Bones helped Jim by talking with him, the way Tiberius did. By the time of graduation, Jim passed all his psych evals successfully – he learned how to deal with his issues, now he knew how not let them control him. He even got rid of some.