Where were you when the Twin Towers were hit? When the bank guarantee was announced? When the Princess of Wales died? I don't suppose too many people remember where they were when they first heard the coronavirus or Covid-19 mentioned. But it is epoch-defining. And it will impact personally on us all, in large ways and small.
Self-isolation and social distancing are new terms we are becoming familiar with - new ways of interacting with one another. And more stringent restrictions are on their way.
"Tighten the valve. Tighten the valve more. If the number doesn't slow down, close the valve. We're closing the valve." That's how New York Governor Andrew Cuomo describes lockdown in New York City, hotbed of the pandemic in the US.
Here in Ireland, perhaps some people feel their liberty is being curtailed in a harsh and excessive fashion. Maybe they feel their inability to move about at will is an unacceptable infringement of their civil liberties.
But this is a pandemic. If a lot of people catch the virus simultaneously and need to be hospitalised, they'll collapse the healthcare system. Already, some 25pc of confirmed cases are health workers, which adds pressure. And there are reports of medics running out of goggles, masks and gloves - even before the anticipated surge happens.
Isolation restrictions imposed in Ireland bear no relation to quarantine in China. I've just spoken with my niece there, who's been confined to a hotel room as a precaution. She was tested three days ago for Covid-19 - the result returned in 12 hours and was negative - but she must still do the full 14 days of lockdown. Currently she is on day 11.
When Louise Devlin returned to China to take up her teaching job, after going on holiday to Thailand during a two-month-long schools closure, she was given a throat swab at the airport. Then she was driven to a designated hotel and forbidden to leave the room for any reason.
Her temperature is checked twice daily and food is delivered to her door three times a day. Someone knocks to let her know her meal is on the mat and she must wait before opening the door so the delivery person has time to leave.
Louise (33), a teacher in Nanjing, a city some 300km from Shanghai, says: "What you have in Ireland isn't lockdown as we know it. You're able to go out for walks and to buy food - I can't leave this hotel room. It's really strict. The government imposes the rules, nobody gets to question them.
"At least I have internet but the day is very long. The people I really feel sorry for are those quarantined in hotel rooms with their children - you can just imagine how bored the kids get.
"And I'm lucky I have a window. My big happiness is being able to open it - I was afraid I wouldn't be allowed.
"It's isolating because at no stage in the day does anyone touch you. We're social animals. We're used to touching with our hands, or handing over things to one another. I can't have a conversation face to face with anyone during quarantine."
The only human contact she has is when her temperature is taken. There's a knock on the door, she stands in the doorway and someone shines an infrared monitor on her forehead. The person checking her wears a visor covering their face, with a mask over their nose and mouth underneath it.
"It's a faceguard like a welder would wear but made of plexiglass so it's clear," says Louise. "They also wear gloves and disposable plastic gowns like you see in hospitals. They are very polite and nice although they don't speak much and I miss that. Sometimes they'll say, 'OK - that's all' - or let you see your temperature reading so you know it's normal."
Omagh-born Louise, who has a Master's in chemistry from UCC, has been allocated a government health code, a QR code, on her mobile phone - mandatory when people arrive in China. Currently it's red but she's been told it will turn green at the end of quarantine.
"I'll need to show this green code every day at the barriers they've put up outside the school where I'm teaching, before I can get in, and also for entry to restaurants and supermarkets," she says.
"When you're in China you have to assume your civil liberties aren't what you were used to. Everything is being monitored. They know where everybody is and who they've been in contact with.
"What bothers me is the level of monitoring after this outbreak will continue. They've stepped it up now and aren't going to stop."
Another worry is that even if her green code comes through, it won't be accepted generally.
"I've heard that people with it are being turned away from restaurants. "We don't want you," they're told. People are crossing the street to avoid foreigners.
"There is quite a lot of racism towards foreigners because of the imported cases of the virus in the country. The rest of the world is now the danger zone to the Chinese. The news is carrying reports that outside cases are the problem.
"Because you're a foreigner they're worried that you're lying about having been quarantined or you're breaking the rules in some way. I just wish they didn't have different standards for foreigners and nationals. Most people on the street are not highly educated and so it's not their fault they equate foreigners with bringing it (Covid-19) into the country."
She knows of a man from Tipperary who's had to go into a higher level of quarantine because someone was sitting within five rows of him on the plane returning to China and tested positive. That's how severe their policies are. In such cases, the people taking temperatures wear the full hazmat or biohazard suits and all waste is disinfected.
Even when home quarantine was allowed, it was more severe than the Irish version. A community worker met people and took them through everything they were meant to stop doing. Someone visited daily to check the quarantine was being observed and magnetic strips were added to doors to monitor how often they were opening.
Louise's quarantine is up on April 1, which also happens to be the day she's due to return to the classroom.
"That's April Fool's Day," she says. "I hope they don't play a joke and let me go, then take me back again."
When she's back teaching, she's been told she'll have to take extra classes because of a teacher shortage caused by quarantine restrictions. China has announced it is sealing its borders to most foreigners from today.
But on the plus side, Louise says that life is returning to normal after two months. And the same will happen in Ireland, given time.