Those of a certain vintage remember where they were when they heard John F Kennedy had been assassinated. Likewise, the attack on the Twin Towers in New York provoked images of catastrophe which lives on in the minds of a later generation.
It is obviously not on the same scale but the announcement that British Prime Minister Boris Johnson was rushed to an intensive care unit is an event which also stopped many in their tracks. It will remain in the memory banks of those who, in whatever guise, are facing down Covid-19.
The physical deterioration reflected in Mr Johnson's pallor was played out on national television. The prime minister, so dismissive of the virus early on, was clearly in its clutches.
Reports suggest he is now on the way to recovery but medical experts warn those who spend time in intensive care must cope with physical and psychological scars.
Will Mr Johnson's time among the seriously ill and dying change his life forever? He was obviously very sick and the shock to his senses over recent days is an experience like no other in his life so far.
Everybody is fashioned by mould- breaking events which make and unmake them. Mr Johnson can be no different. Will, for example, his trademark bullish dogmatism be tempered by those moments of forced introspection spent on his hospital bed?
He would have seen doctors and nurses moving about, masked in a kind of space-age protection now familiar to us all. Hushed tones would tell of high stakes. Challenges and choices abounded. The ultimate fight was the fight for life itself.
The public shock at the prime minister's hospitalisation is that he was clearly outside the coronavirus high-risk group. Aged 55, he is a non-smoker and is believed to be a moderate drinker. While somewhat overweight, he had no known underlying symptoms that may have made him susceptible to serious illness.
His high profile is a reminder that seemingly sound health - and in his case status and wealth - is no protection for those with a cavalier approach to this virus. No wonder his unexpected hospitalisation shocked the British government to its core.
Britain's axis of power is centred in a narrow complex of buildings ranging from 10 Downing Street to the Houses of Parliament. Mr Johnson and his ministers, protected by their own cocoon, convinced themselves they were immune to infection.
Social distancing suggested by medics was initially dismissed as over-reaction. A prevailing wisdom among some in the prime ministerial inner circle was that the disease would eventually work its way through the system. All would be back to normal in a matter of weeks.
This, however, proved a forlorn hope. Valuable time was lost. It left the UK authorities on the back foot as the Covid-19 death toll began to inexorably rise.
Mr Johnson must be confronting myriad emotions. How will what could have been a near-death experience affect the most gung-ho politician of recent times? Will his cultivated sense of over-optimism come unstuck? Could it be the chutzpah of old will be no more?
His troubled childhood and teenage years fine-tuned a coping mechanism which dominates his personal and political persona. Basically it is a kind exuberant can-do philosophy. We have all become familiar with a bluster which is essentially meaningless.
It is a modus operandi too often based on deceit, lies and self-delusion. Commitments are made and then broken. He especially seems to be devoid of any sense of loyalty.
These perceived character deficiencies are of course not unknown among politicians. Indeed, some cynics may suggest they are intrinsic to survival in the dark trade.
However, the prime minister's sense of his own mortality has been questioned. This will surely challenge the innately glib side to his character. Might he now become a more thoughtful and reflective politician? From the viewpoint of this country, it might mean in future we are confronting somebody less inclined to deal from the bottom of the deck.
The great American songwriter John Prine was taken from us this week by the coronavirus. He once said: "There's only two things. There's life. And there's death." Perhaps that's a bit maudlin. But a reborn Boris Johnson would understand.