There's this New Yorker friend of mine who'd been into a promising start-up exporting seafood from China to the United States, when the 9/11 attacks upended everything. His business had invested scarce capital to join September trade fairs around the country to secure new clients and orders for Christmas sales.
Instead of the breakthrough moment expected, the trade fairs were cancelled and the business was out of cash. He decided to close the company.
With airlines grounded in the aftermath of the terror attacks, a planned holiday to Florida with his in-laws became a road journey.
Watching the cable news television images play on a constant loop, showing the same picture of terror mastermind Osama bin Laden in a combat jacket and with gun in hand, below a turbaned head, my friend recalls the bemused response of his in-laws: "Why doesn't he wear a baseball cap like the rest of us?"
Bewilderment that anybody could so hate America combined with anger and vengefulness. From that point on, America, and the world, would change forever.
"Americans suddenly realised that the outside world mattered to them," says Mr Drew Thompson, a visiting senior research fellow at the Lee Kuan Yew School of Public Policy, who is from New York. "And a new phrase would become permanently etched in their consciousness: homeland security."
Osama's masterstroke - to the world's great good fortune, the Twin Towers were less than half occupied that early in the morning when the planes struck - would trigger a series of reactions. At one time, more than half of the Federal Bureau of Investigation's (FBI) officers were investigating the attacks.
Deputy Secretary of State Richard Armitage famously threatened Pakistani leader Pervez Musharraf that the US would "bomb you into the Stone Age" if Islamabad didn't switch loyalties and support the coming US global war on terror. Mr Musharraf's intelligence services had close links with the Taliban, whose protection helped Osama thrive in Afghanistan.
Then the war began, delivering what the US believed was "shock and awe". The Taliban fled into the mountains, and into Pakistan. At one point, the US-led coalition in Afghanistan numbered 130,000 personnel from 50 countries.
Within the militant Muslim framework, competitive terrorism manifested. The Bali bombings of 2002 took more than 200 lives. Six years later, there were bigger headlines when more than 160 people perished in attacks on luxury hotels and a railway station in Mumbai.
The 9/11 strikes also hurt civil aviation. Global airline revenues did not go back to 2000 levels until 2004. Neither did passenger traffic.
Architecture would change in more lasting ways.
Mr Hasan Syed, a Shanghai-based design director at giant US architectural firm Gensler, told me there had been dramatic changes to building security and safety. "Just one instance - now it is standard to have refuge access every 10 levels, rather than one in 15 levels," he says.
Functionality, not prestige, is stressed at every level. Suzhou Zhongnan Centre, which he's just completing, was scaled down from 729m to 500m, to comply with new Chinese regulations on building heights.
Society would undergo dramatic shifts, starting with widespread Islamophobia but also a corollary - white nationalism and terrorism - sometimes in unlikely corners.
Mr Ali Soufan, the legendary former FBI special agent who tracked down hundreds of Al-Qaeda terrorists, told me two years ago that between 2009 and 2019, more than 73 per cent of terrorism-related deaths in the US were due to groups like those made up of white supremacists and right-wing extremists. "These two dangerous networks feed on each other."
The New Zealand shooter who attacked two mosques in March 2019, killing 51 people, claimed to have had "permission" from a man sitting in a jail in Norway - Anders Behring Breivik, the far-right white nationalist convicted of the 2011 mass murder of 77 people.
Ordinary, peace-loving Muslims would be even more troubled.
"9/11 shook the Muslim world," says Singapore businessman and former Nominated MP Zulkifli Baharudin. "They were frightened of being accused of carrying an ideology they did not agree with."
To the credit of the Muslim community worldwide, Muslim families and community leaders often came forward to point out community members drawn to extremist thinking.
Still, the expansion of the war into Iraq and Syria, and the bestiality often involved, also triggered resentment against the US. Recent videos of Taliban members performing the Sajdah Shukr thanksgiving prostrations after the US pullout went viral among Asia's Muslims.
It is impossible to overlook the slipshod way in which US President Joe Biden ended the war.
"The moral of the story is, don't help the Stars and Stripes," gleefully tweeted Ms Margarita Simonyan, editor-in-chief of Russia's RT broadcaster. "They'll just hump you and dump you."
But the world should be grateful to Mr Biden for standing against establishment advice and going through with the pullout. Wars, it is said, are easier to start than to end.
Today, when we count the costs of the "forever wars", this is what we see: 37 million refugees, thousands of Nato troops dead - more than 7,000 US servicemen top that list - and some 50,000 wounded.
An estimated 30,000 serving and retired military personnel ended their lives because of the horrors they participated in or witnessed in theatres such as Afghanistan and Iraq.
To be sure, the war on terror was not without its successes.
The most spectacular, of course, is that the US hunted down and killed Osama in a Pakistan safe house in 2011. US strikes also eliminated Abu Bakr al-Baghdadi, the leader of the Islamic State in Iraq and Syria (ISIS).
Either thanks to luck or fabulous intelligence, the US mainland has also escaped a mass casualty terror strike planned from outside.
Mr Syed, the Gensler architect, points out that more skyscrapers were planned or executed in the two decades after 9/11 than in the two decades prior to it.
But it is equally important to note that societies were ruptured or disrupted in other ways.
The US elimination of Iraqi leader Saddam Hussein, using false reasons, gave an opening to ISIS. The Syrian civil war, partly supported and armed by the US, took more than half a million lives.
Stunningly, the world came to accept that intrusive state surveillance was an inevitability. Recent revelations that about a dozen governments used the lethal Pegasus software developed by Israel's NSO Group to spy on people in 45 nations hardly drew a gasp.
Still, no one doubts that terror thrives. The Singapore Terrorism Threat Assessment Report released in June says the threat to Singapore remains "high".
Globally, the report adds, terrorist activities have persisted amid the Covid-19 pandemic, with terrorist recruitment and propaganda efforts stepped up online.
One result of the 9/11 strikes had been that accelerating geopolitical tensions between the US and China took a pause, and there was even a period of cooperation that continued through the global financial crisis of 2008.
But it was clear even before Mr Xi Jinping assumed the Chinese presidency that the big-power relations would soon slide, as they have.
Today, the US is energy self-sufficient. Its interest in the Indo-Pacific region is partly so that it can control a big portion of China's energy supplies at source.
Afghanistan is squarely a problem for its neighbours and near-neighbours - Pakistan, Iran, China and Russia. The US is confident it can identify and neutralise any threat to the homeland emanating from there.
The 2018 Schriever Wargame by the US Air Force Space Command had hints of the next likely theatre of conflict. It gathered civilian and military experts from 27 US agencies, joined by experts from Japan, Australia, New Zealand, Britain, France and Canada.
Using a 2028 scenario, it included a global scenario with the focus of effort towards the US Indo-Pacific Command Area of Responsibility.
Mr Biden's stated intention with the Afghan pullout was to end the forever war, as it is called.
Technically speaking, though, there is an even longer war - the Korean War, which never ended with a formal peace treaty. The US still maintains some 25,000 troops in South Korea, and Mr Biden has no intention of withdrawing them.
One war may have ended, but conflicts remain. It's a small measure of relief that Mr Biden and Mr Xi spoke this week after a long interval, in a bid to set guard rails to manage the US-China relationship.