How does he do it? What's his formula? And what does the stress of coaching do to his psyche?
He's thought about all that a lot and Correspondent Mike Wallace put him on the couch to talk about it -- as he never has before.
To begin with, Parcells told 60 Minutes that one big secret of his success has been head-to-head confrontations.
"I think confrontation is healthy, because it clears the air very quickly," says Parcells. "And most of these athletes that you deal with are pretty well used to that kind of thing."
Has an athlete ever taken a swing at him? "Oh, yeah," he says. "We've had a few of those. That's OK."
Parcells spelled out his notion of how to turn a loser into a winner in The Harvard Business Review. He wrote that a new coach, or a new CEO, has to wage a relentless pursuit of perfection by showing he's in charge -- by imposing his leadership.
And of course, confrontations can do that. But in Parcells' case, it resulted in one of his players throwing his jersey in Parcell's face, and being taken off the field by security.
"These things happen," says Parcells, who adds that the player is still on the team. "I don't have to make examples out of players to establish my own place. I don't feel like I have to."
"You mean everybody knows what a prick you are?" asks Wallace. "Yeah," says Parcells, laughing.
When Wallace first profiled Parcells five years ago, he was at his toughest on his players, and on his coaches.
But most of all, he keeps the pressure on himself – 14-hour days, six days a week. And on the seventh day he rests, a mere 12 hours.
Does he really need to work 14-hour days?
"Yes, sir. Maybe more. If you want to stay competitive, this is one of the most competitive businesses there is," he says. "It's my life. It's my blood. It's how I'm measured."
After that season, Parcells had it. He said his coaching fire had burned out, and he retired. But then, last year, at the age of 61, he came back, to spur the Dallas Cowboys to their first playoffs in four years. And nothing had changed.
What excuses does he accept from his players?
"I'm not really in the excuse business," says Parcells. "We have this expression, 'Don't tell me about the pain, show me the baby.'"
"You know, let's get the job done here," adds Parcells. "I don't want to hear about the process."
Officials also wish they didn't have to hear so much from him. Sporting News has called Parcells, "A tyrant, a relentless perfectionist who makes everyone around him miserable."
"The first, maybe tyrant, I don't know. Certainly perfectionist," says Parcells. "But misery? I don't think so. No, I don't think, I don't intend to make people miserable. I am demanding."
But he admits that he's miserable. Why, if he loves the game?
"Someone kinda helped me with that recently, and he said that, 'The gift you have is also your curse,'" says Parcells. "'And then, when you get at a certain place, you're looking for something else that challenges you even greater. And as a result, you become miserable until you find that.' It was never called to my attention so specifically."
It was something that his former wife, Judy, had once called to his attention. Wallace met Judy Parcells five years ago, but they have since divorced after almost 40 years of marriage.
Did coaching kill his marriage?
"I would never blame it on my job. I would blame it on myself and the way I was negligent in a lot of respects," says Parcells.
Wallace played Parcells an excerpt from their last interview, in which Parcells said: "First of all, this is no disrespect to my wife Judy, because she's been in this for a long time. Judy doesn't know whether the ball is blown up or stuffed with feathers, OK?"
Parcells laughed, and said, "I didn't mean, literally. I just meant that Judy never worried about the -- she couldn't be capable of worrying about the depth of [my misery.]"
"She would ask you why you kept coaching," says Wallace. "She says, 'The times that you're happy are so few compared to the times that you're unhappy. Why do you keep coaching?'"
"It's difficult to explain. But this game and this business is not without a myriad of incessant problems," says Parcells. "Even when you're successful, even when you win the game, about an hour after the game, you have a litany of things that you now deal with that are problematic. ... So the times that you are happy are minute compared to the time that you're dealing with problems."
So why did he come back for more misery after just three years of retirement? "I was just starting to get a little bit bored," says Parcells. "That thing that's always reached out to me, to bring me back. It's been a long arm. It's a tentacle. It gets you. And it drags you back in."
The tentacle that dragged him back was the long arm of Jerry Jones, the Cowboys' all-powerful owner, known for riding coaches hard, and then firing them. He's fired five coaches.
"I was basically perceived as someone that was difficult to work with," says Jones. "That was difficult for coaches to do their job. I am involved, was involved hands-on."
But with Parcells, Jones has to be more hands-off. Jones had made his fortune in oil, and with it, he bought America's team - the Cowboys - and won three Super Bowls.
But when the Cowboys collapsed, and had three losing seasons in a row, Jones was desperate to hire a winner. He's paying Parcells $17 million over four years.
"The expectations that I place on what we do as a team, and I know our fans are expecting, those can be very nerve-racking," says Jones.
And now, he's trying hard to defer to Parcells, but it doesn't come naturally. "I think -- I'll call him the boss," says Jones, who will keep placating Parcells as long as the coach keeps winning.
"I work hard at making this work. And I've involved our entire organization in a way that makes this a good experience for him," says Jones. "I'm tempted to use the word pleasant. But you can't use that word in football."
And you can't use that word with Parcells. "Bill is prickly," says Jones.
But "Prickly Bill" has given ground, too, allowing Jones to walk the sidelines -- even though he has long said owners do not belong there. And on some subjects, like superstition, here's a story.
"Jerry Jones told me that you chewed him out because he leaned over and picked up a coin, a nickel on the ground yesterday. Why?" Wallace asks Parcells.
"I'm a little superstitious. You don't wanna tempt fate now," says Parcells. "I had an Italian mother. She was very superstitious. It's a real thing, you know. Superstition. People think it's fake. It's not. It's real."
Now about the coin. Parcells says it had the tail side up. What if it had been heads up? "Well, do you wanna be on the back end or the front end of things?" asks Parcells.
To stay on the front end, Parcells picks players who share his passion, like confrontational Keyshawn Johnson.
Johnson told 60 Minutes that Parcells' pressure helps him excel - but that some players can't take it.
"We had a guy quit recently in camp because he just wanted to get away from Bill Parcells," says Johnson. "Told Bill he couldn't do it anymore. I think Bill told him to go ahead. 'Adios amigos!'"
Quarterback Vinny Testaverde had his best season playing for Parcells back with the Jets. Now, even though he's 40, Parcells signed him to lead the Cowboys.
"He tries to put a lot of pressure on the players on his team throughout the week of practice," says Testaverde. "So, when you go out on Sunday afternoon and play in a game, it's like the world has been lifted off your shoulders."
But while practice can be excruciating for his players, Parcells told 60 Minutes that the practice field is the only place he feels truly at home.
"That's my favorite place out on the field. Practice field," says Parcells. "It's my sanctuary. I feel cloistered there."
And on that field, he let Wallace in on a secret. At the ripe old age of 63, he believes that has finally started to mellow.
"You know, the end is near. I really do know it, you know what I mean," says Parcells. "So I can enjoy it more. I'm enjoying it a lot more now than I did and I'm not beating myself up quite as much."
He told Wallace that he and his veteran players aren't just fighting the opposing team -- they're fighting Father Time.
"We're all in the same boat. Testaverde, Keyshawn Johnson, Bill Parcells. All of these kids, we're all at risk," says Parcells. "They're all waiting to say, 'You guys are washed up.' They're all waiting to say it. That's the business. But that's also the fun. The fun is trying to prove somebody wrong."