"It's not the pandemic we had to have, but it has shown our character under a harsh spotlight," he says.

"There will be people who carry damage forward, there is no doubt, but what a trial for our nation.

"I'm very proud of what we've done and despite the horror of the coronavirus and the economic downturn, we have to tell ourselves that it will only make us stronger."

He wants us to think about previous generations who lived through the Depression and two world wars, but were the ones in charge when Australia really began to emerge as a nation in the 1950s and 60s; he wants us to take that optimism into the future as we begin tentative steps towards 2021 and beyond.

"We have to ask ourselves: why wouldn't we be stronger? We might be a little more cynical, but we coped, so we'll cope with whatever life throws us next," he says.

For Cosgrove that means, when things return to normal, spending more time travelling with his beloved wife Lynne - "the moment I married her I became a better person" - catching up with his children and grandchildren, and heading back to Canberra for coffees with lifelong friends.

You Shouldn't Have Joined wraps up the official Cosgrove written story - "there will be no more books about Lynne and me" - following on from 2007's My Story and 2011's A Very Australian Conversation, from the Boyer Lecture series.

This book is much like the man, full of empathy and humour and considered opinions on everything from climate change and whether or not Australia should be a republic to the state of Australian rugby union and the Seekers.

At 73, Cosgrove is grateful for the life he's had. As a kid who grew up "a battler on Struggle Street" in Sydney's Paddington, he attended high school at Waverley College, came to the Royal Military College, Duntroon, in 1965, and fought in the Vietnam War, where he was awarded the Military Cross. In 1999, as a major-general, he led the international forces in the East Timor peacekeeping mission and in 2000 was promoted to Chief of the Army. In 2002 he became Chief of the Defence Force.

"As soon as I entered the army I thought 'this is a mistake'. It wasn't working, I was getting into trouble all the time, I was immature and I wasn't meeting the standards of the Australian Army," he says. He was just 18 when he arrived in Canberra, "and I didn't expect getting to my 21st birthday still in uniform".

"Then when I got to be 21, I couldn't imagine getting to 30. Not that I would get killed or anything, but why worry about things that weren't happening now? Maybe it was naive, but also, in retrospect, a bit endearing, because it meant I tried to do every job I had in front of me as if there was no tomorrow.

"I didn't ever set ambitions, I had no goal of getting to the senior ranks until I got to a reasonably senior rank and I'd see the people in the next rank up and say 'I reckon I could do that job'. You'd discover that it wasn't heavenly, Olympian, mysterious, it was just a job done by other people."

While at Waverley College in 1963 he met the then-governor-general, Viscount William De L'Isle, who was the reviewing officer of the cadet program's passing out parade. Had bucket lists been in fashion then, he writes, "I would have ticked off 'meeting the governor-general.'"

Whether or not he was expecting the phone call from then-prime minister Tony Abbott in October 2013, asking him if he'd like to take over the role, he doesn't say. There was some speculation about whom the government would invite to follow on from Quentin Bryce. Sportsbet had Cosgrove at $1.30.

On January 28, 2014, the Cosgroves moved into Government House in Yarralumla, and he became the 26th governor-general of Australia; he was in office until July 2019. A year later it's still a position he's a champion of, saying while there is still some public opinion that it's an antiquated position tied to the monarchy, one which involves plenty of "swanning around", there is much more to the role than that.

He talks about the Governor-General's role in constitutional duties - from granting elections and providing royal assent to legislation to presiding over the Federal Executive Council and the swearing in of new ministers with pride. Swearing people in was one of his favourite duties.

"[It was about] watching the joy of a newly formed government, full of energy and delight and optimism, the relief of having been through an election," he says.

He believes politicians do it for the right reasons, that they want to serve their constituents, their nation.

"It's such a tough, tough job. You're not in it for the easy lifestyle or the money, so there must be a sense of civic duty."

He grew up listening to question time. His mother, an "out and out Labor voter", would do her chores with the radio on. He's met a few leaders over the years. Malcolm Fraser looked exhausted, Kim Beazley was enormously interesting, both John Howard and Bob Hawke, while very different people, had the capacity "to balance the exercise of authorised power and practice of politics".

It's always been important to him, first as a soldier and later as governor-general, that he was "detached from any hint of politics".

"I've been asked a few times, before I was governor-general, if I would consider filling a casual vacancy in the Senate - but my reply was, to misquote Elizabeth Barrett Browning: 'How shall I refuse thee? Let me count the ways'.

"I don't think I have the patience or temperament to engage in what might be called the warp and weft of political discourse."

It's obvious from the book that Cosgrove has thoroughly enjoyed his public life. There have been many challenges, from active service to dealing with natural disasters such as cyclones Tracy and Larry and the Boxing Day tsunami of 2004.

"To this day, that's one of my proudest moments as an Australian - we set to action immediately. Our government and public response to Indonesia's need - even though our relationship with them could have been somewhat jaundiced for a variety of reasons - was the greatest of all contributing nations. We put those attitudes aside and said 'this transcends that, these are our neighbours in need'."

He agrees that in some way, that is what 2020 has been about as well. Australians banding together to get through something unprecedented. His advice for those of us who are wondering where our lives - and the country - are going is to remain optimistic.

"If you're thinking about what you're going to do next, do something you love and do it well, take the satisfaction from that and see where it leads you," he says.

"And rejoice in being an Australian. Whether it's true or not, we do believe we're unique - and I think that's a marvellous thing for a nation.

"You don't want a nation to say: 'We're one of many, no different to anybody else.' Let our conceit be that we believe we have a highly developed sense of cohesion and compassion."