On a sunny Sydney morning, Bill Bryson is sitting on a squishy couch and explaining why he is not allowed to have a fancy mobile phone. "I would lose it in 10 minutes," he says. "I always lose my phones. And I don't want the responsibility and the despair of it."

He has spent years "making personal gifts to the world" of fancy phones, so he stopped having them. "Well my wife stopped me," he says. "She doesn't permit me to have anything decent. She has a nice phone now. She sometimes lets me hold it and look at it."

Bryson, best-selling author of self-deprecating accounts of his travels through Europe, the United States and Australia, not to mention acclaimed books on science, language, Shakespeare and his own childhood in Iowa, is visiting to discuss not a new book but a 17-year-old one.

A Walk in the Woods: Rediscovering America on the Appalachian Trail, has been adapted into a Hollywood film starring Robert Redford, Emma Thompson and Nick Nolte. The best-seller, published in 1998, tells the story of Bryson's trek with old friend Stephen Katz (a pseudonym).

The film, A Walk In the Woods, follows Bryson (played by Redford), tired of "life being all about ailments and funerals" and deciding to trek the 3200-kilometre Appalachian Trail, the longest continuous footpath in the world. The trail, which takes five to seven months to complete, traverses 14 states and crosses the Smoky Mountains, Shenandoah National Park, the Great North Woods of Maine and the Berkshires.

Of the 200 hikers who attempt it each year, only 10 per cent make it. Encounters with bears, moose, rattlesnakes, blizzards and poisonous plants are a regular occurrence. So are run-ins with other hikers of irritating good cheer and know-it-all efficacy, as the film highlights.

Bryson and Katz, the latter recovering from alcoholism, haul their oldish bones through snow storms, bear attacks, romantic temptations and perilous cliff-edge scrambles. They also explore "lost and regained friendship" as Redford called it at this year's Sundance Film Festival.

Initially A Walk In the Woods was to be a reunion movie for Redford and Paul Newman. The idea gained momentum for two or three years but Newman became ill with cancer and died in 2008.

After nearly two decades of development, Bryson says the film is terrific – and true to the spirit of his book. Nolte and Redford's on-screen chemistry is clear.

"I've had – sincerely and completely – complete confidence in the whole project because of Robert Redford," he says. "My only fear, mildly paranoid sort of fear, was that somehow he would lose interest in it and that it would get sold on."

Watching himself being portrayed by Redford was "definitely surreal" but only for the first few minutes. "And I was surprised by that," he says. "I thought it was going to be surreal for quite some time, but it was really only the first time when he opened his mouth. When the television interviewer character in the opening scene said, 'And our guest today is Bill Bryson', and it was Robert Redford, that was a little surreal.

"But it very quickly became me watching this. At no point was it really my life. I think partly it was because both the book and the movie that came out of it are only fragments of my experience. If it had been the Bill Bryson story, my childhood in Iowa and all of that, I think the fidelity to actual events would have been more important. But they were just recreating, in a completely different guise, five months of my life.

He had no problem with the fact that the film gives him one child, where in reality he has four, or that his wife's name has been changed. "In this particular kind of movie I can't see that that makes one tiny spit of difference at all," he says.

Bryson's curiosity about the project was mainly about trivial things. How would Hollywood set designers depict his house? Particularly when they had never seen it.

"They wanted to come and take pictures of our house and they wanted me to describe in detail what my home office was like. I told them it was basically none of their business," he says. "Just imagine it.

"So it is all imagined."

As it happens, the house in the movie, and the overall look of the recreated Brysons' private life, is not far from the truth. Bryson's home office does not feature the objects that surround Redford as he types, but the photos on the wall are pretty close, showing events from Bryson's life.

"This could have been our house," he says. "It was just interesting to see how people who know nothing about you imagine how you are."

The overwhelming impression upon meeting Bryson is of a very nice man. His smile takes over his whole face when he laughs. But he does not suffer fools gladly, as any reader of his books will know.

As readers will also know, he appreciates the beauty of the world, what life has given him and how lucky he is. "You know, you only live once and we really ought to make the most of it and we ought to be happy," he says.

In a lecture he gave in London in 2010, he identified "the four most remarkable things I know". The first one was: "You exist. You're alive."

A Walk in the Woods, with its tale of two old friends pushing for adventure late in life, underlines the importance of that fact. "It was supposed to be a book about an experience, about the challenge of hiking and the pleasure of discovering the great outdoors and all of that stuff," he says. "But it did become a book about an experience, about bonding. Which I think, for men, is an unusual experience.

"Women do it instinctively, all the time. All women have at least one or two really close friends and they tell them everything. Men don't tell anything personal to any other man, ever, hardly.

"Men don't talk about their feelings so much and women get frustrated with their husbands because they just want to watch television and not talk about their feelings. I have eavesdropped on my wife's conversations with friends at times and I just think, it's just amazing the things they talk about.

"They're nearly always talking about feelings and emotions and connections and, you know, really concerned about, 'What did she mean when she said this or that?' Men would never do that. I mean, we are just basically cavemen. We just want to be fed and watch football."

He still likes travelling, he says, and it amazes him that he does. He never intended to spend so much of his life visiting new places and writing about them. He calls himself "a terribly incompetent traveller" but loves flying because there are no phone calls or interruptions and he can work on his laptop in peace.

The reason he has been able to achieve so much, he says, is his wife, Cynthia. Not long after Bryson first arrived in Britain as a 22-year-old backpacker, he got a job at a psychiatric hospital in Surrey. There he fell in love with Cynthia Billen, a psychiatric nurse. They have been married for 40 years. Often when he travelled, Cynthia stayed at home, raising their children.

"She's very patient with me," Bryson says. "I think I'm a fairly equable person, I don't think I'm hugely difficult to live with. But, like most people, I am an idiot. All wives know their husbands are idiots. And I think a bit vice versa as well. So she's been very patient with me for a long time."

Does she still dust him down when his jacket gets dirty, as described in Notes from a Small Island? "Yeah, yeah, yeah. She does all of that. I wish she was here because she always does straighten me out, comb my hair down, tell me I've got egg yolk on my collar.

"She came with me on my last trip to Australia and we built in some spare time. We did mostly Victoria on that trip, so we did the Mornington Peninsula, we did the Great Ocean Road. It was great for both of us."

Bryson is a big fan of Australia, having visited regularly and written about it in the best-seller Down Under, published in 2000. "I don't think I've been anywhere in Australia that I didn't like a lot. But I'm particularly fond of Sydney and Melbourne. I think they're two of the world's greatest cities.

Sydney and Melbourne do like each other, he says, "but you just won't admit it".

The first chapter of Down Under begins with Bryson realising "with a sigh" that he has once again forgotten the name of the Australian prime minister. Can he remember who it is today?

"Mr Abbott," he says, smiling. "I know."

The last one? "Oh God, was it Julia? Did she replace Rudd? I do lose track because you've had quite a lot of turnover. I don't follow what's going on in Australia and then I come back and I discover all this stuff that's been going on.

"I'm intensely interested in all the things. I pick up the paper and immediately I want to know everything there is to know about Bronwyn Bishop and all these stories. And then, of course, I'll go away on Friday and I'll forget about it."

Is he an optimist? "Yeah, I think I am. But against all the odds. You look at things like Donald Trump and you have to be an idiot to be terribly optimistic about some things.

"But I do, by and large, at least in my personal life, try and be optimistic. And grateful and pleased to have it."

A Walk in the Woods opens on September 3. Buy the book now on Booktopia