When he was in his fourth year of medical studies, O'Sullivan and his wife Tracy had their eye on a Dunedin four-bedroom bluestone villa with 10 acres attached, but he could not get permission to transfer from Auckland University to the Otago School of Medicine.
As O'Sullivan says himself, had they moved south, the story could have turned out ''very differently''.
And what a story it is.
Who would have thought the troubled teen, with a largely absent and alcoholic Maori father and determined but embattled Pakeha mother, would turn out to be a national hero, showered with accolades for his health and community leadership in the Far North?
He is the outspoken GP who got into hot water with his employers when he refused to turn away people who couldn't pay for his services.
O'Sullivan and Tracy, whose background is in nursing, are now running their own medical centre in Kaitaia designed to cater for the largely Maori community they serve.
They have a walk-in clinic so patients can turn up at a time to suit them, employ non-medical staff kaiarahi (navigators) to support and guide patients and make the most of opportunities to use telemedicine in remote areas.
Nobody is turned away if they cannot pay.
Written with Margie Thomson, O'Sullivan's account of his life is honest and often moving, particularly over his yearning for a close relationship with his father.
And while it is a story of a remarkable man, the continuing influence and importance of the women in his life - his mother Marlene O'Sullivan (originally from Timaru) and Tracy, who became pregnant with their first child when he was 20 after they had known each other only three months - shines through.
Father-of-seven O'Sullivan tries hard to set a good example in all he does.
He cycles 15km to work and rarely has a beer these days, having gone largely alcohol-free for eight years.
He feels strongly about the harm caused by alcohol throughout society and the fact the health burden of alcohol falls inequitably on Maori.
He supports higher taxes on alcohol which could ''bring alcohol back to being a privilege and a treat, rather than an everyday event''.
He does not claim to have all the answers, saying the ''jury is still out on what a health system that truly addresses indigenous needs in Aotearoa would look like''.
However, he is not frightened to pose some hard questions about health care, such as whether we spend too much money on surgery for very elderly patients which could be better directed elsewhere, and the wisdom of spending $30,000 or $40,000 on medications for a man who really needs ''a lifestyle coach'' to work with him to change unhealthy habits.
It is an uplifting, stimulating and hopeful story which deserves to attract wide readership.
Royalties from the sales will go to the Moko (Manawa Ora, Korokoro Ora, or healthy hearts, healthy throats) Foundation, a charitable trust set up by the O'Sullivans to support and empower communities, with a focus on vulnerable children and young people.
• Elspeth McLean is an ODT columnist and former health reporter.
