Nelson is 31, tall, slim and articulate, a grown man with a family and, for when boxing ends, a teaching qualification. Douglas is a bespectacled, neat 38-year-old who has enough money to live without fighting. Yet neither can move on to the rest of their lives without laying the past to rest.
Douglas boxes today, the seventh fight of what is not so much a comeback, more a personal redemption. In 1990, he felt the exhilarating high of knocking out Mike Tyson. Then his world collapsed. Although he was paid a gross $24m to defend the world heavyweight title against Evander Holyfield, he was an uncomprehending figure at the centre of a ferocious power struggle between boxing promoters and Las Vegas casinos.
One way and another, his pay day was torn apart. Long before he stepped into the ring against Holyfield, he realised nobody gave a damn about him, felt the anguish of betrayal, and flopped. Even his own father said the knockout punch wasn't that hard.
He took his money, and got out. But the experience had weakened him. Always inclined to stack on weight, he meekly ballooned to 400lb and collapsed in a diabetic coma. He remembers waking to hear doctors talking over him as if he were a piece of meat. He could have died then, but decided not to.
Now, after shifting more than 150lbs, he is boxing again, because he needs to say something. Ideally, he would love to fight Holyfield, but more than that, he wants to show the world that he's a man worth something more than dollars.
On Saturday night at Hillsborough Leisure Centre, in Sheffield, Nelson fights what he hopes will be a warm-up for a shot at Carl Thompson's World Boxing Organisation cruiserweight belt. It is a pay-day which is not to be undervalued by any father of three kids under seven, but for Nelson its real significance is that it has taken him closer to the victory that would relieve him of the burden which has weighed him down for the past eight years.
If ever a man had a world title there for the taking, it was Nelson on a snowy night in Sherfield in January 1980. In front of him was a Puerto Rican veteran, Carlos De Leon, who was so old he creaked. Nelson could have moved around the ring all night, peppering the old man with quick punches. It could have been as easy as any gym workout.
Except that, after an extravagant vault over the ropes, the young man who called himself "The Entertainer" froze. After 12 miserable rounds, the judges came up with a draw.
It was depressing, dismal, an insult to those who paid to watch him, and worse, an insult to Nelson's considerable talents.
"I was young, scared of screwing up, a boy in a man's body," he will say of that excruciating night, which he must have relived a thousand times. It is true. For that hour he was not a professional fighter, but the shy 15-year-old who first hung around the edge of Brendan Ingle's gym in Sheffield, the nervous amateur who lost more than he won. He needed sympathy, but the hard world in which he chose to live and perform slaughtered him.
Ingle understood, eased him back and in 1992 he was given a second chance in Virginia against another mediocre champion, James Warring. He knew what he had to do, but hid behind some kind of personal plan. He froze again, trailing miserably through 12 rounds, losing on points.
He refers to the years which followed as "my exile". He fought in Corsica, then South Africa, Australia, New Zealand, Thailand and Brazil. It was as if he couldn't get much further away. In 1993, he seemed cold, withdrawn. "I go wherever the money is, my friend," he told me, who was not his friend.
He held titles that nobody cared about, and re-emerged only in 1996 when he signed an agreement with Frank Warren, who promotes all the fighters in Ingle's gym. He is a changed man. He outclassed the veteran Dennis Andries for the British title, and has already won the European crown once, which was then taken from him when he sustained a back injury and could not honour a commitment to defend it in December.
Now he is homing in on a showdown with Thompson, the man whose career came alive with his thrilling win over Chris Eubank last month. Nelson, who is utterly confident he is the better man, can't wait to erase the nightmare. "When I screwed up, I did it big time," he says. "I let myself down, let people down. I've taken too much stick to mess up again."
The point has been made. Nelson's opponent, however dangerous, should understand that men who can fight back from the horror of public humiliation are extremely difficult to defeat. Ask any of them.