Nearly everyone remembers where they were when John F. Kennedy was shot. Likewise, most people in Ireland will recall what they were doing when the police attacked demonstrators in Derry on this day 30 years ago and lit the fuse that started the Troubles.
The present writer was a wet-behind-the-ears seasonal worker in England, squirrelling away a few pounds to get him through the winter when he returned to college in Dublin.
Word of the Derry events came via English friends and fellow-workers who had seen the TV footage. People thought it was a great laugh: the "Paddies" fighting among themselves as usual.
But the subtleties of the Northern situation were never much appreciated on what unionists call the "mainland". Neither are many young people today aware that, before the Troubles, there was a non-violent movement which included Protestants as well as Catholics and sought to change society without resorting to the gun and the bomb.
The injustices which sparked the civil rights movement were recalled by the man who became its most prominent leader, Mr John Hume, addressing a symposium organised by the SDLP's youth wing over the weekend in Belfast.
Had the unionists been more responsive to the demands of the nationalists for fair play, we might never have had over 3,500 deaths as well as 30,000 people maimed or injured. Mr Hume pointed out that, in a population of only 1.5 million, one person in 50 was injured while one in every 400 or so died as a result of the Troubles.
Like a good teacher of the old school, Mr Hume repeats simple but profound messages until, as he puts it himself, "a fellow in a pub says it back to me".
Holding forth to an audience which was not even born when the police drew their batons in Derry, Mr Hume reiterated his view that territorial unity is less important than agreement between the disparate traditions: "Even this beautiful island is only a jungle if people are not united."
It's a message which in some ways lies at the heart of the Belfast Agreement: nationalists have put unity on hold pending the agreement of a sufficient proportion of the unionist population.
The agreement received the support of 71 per cent of the North's population in the referendum last May but this was not reflected among the attendance at the conference of the Young Unionists taking place simultaneously on the other side of the city last Saturday.
Young SDLP activists tend towards jeans and sweaters but virtually every delegate at the (mostly male) Young Unionist conference was arrayed in his best suit. The politics were almost unremittingly hard-line.
Mr Peter Weir, an articulate and forceful Assembly Member for North Down, set the tone for the debate on "constitutional affairs", outlining a series of stiff conditions for Sinn Fein membership of the executive including, not just decommissioning, but IRA disbandment.
The "baby barristers" - as their opponents snidely describe the Young Unionists - had done no favours to the party leader by inviting him to speak at the end of this debate. As the discussion wore on, his few friends in the room must have trembled for Mr Trimble.
But when he arrived - greeted as "First Minister" rather than "party leader" - Mr Trimble looked neither shaken nor stirred. He may have reflected that this would be an easier ride than his last public outing in Portadown where, judging from TV coverage, the crowd nearly did for him.
When he speaks, Mr Trimble is normally in combative mode, usually denouncing the republican movement and all its works and pomps. But this time he was reflective, considered, almost philosophical.
Like a father who catches his young son smoking and proceeds to give him a long lecture about the evils of lung cancer, Mr Trimble told his young audience what he saw as the facts of political life in Northern Ireland today.
It was a revealing insight into the strategic outlook of the UUP leader, leading one to reflect that in some ways the people who had changed most since October 5th, 1968, were not the nationalists, but the unionists of Northern Ireland.
He recalled the words of the late Harold Macmillan when asked what was the most difficult thing he had to cope with as prime minister. "Events, dear boy, events," Macmillan replied. Developing his point, Mr Trimble reminded his young listeners that no one in the position of prime minister (or, by implication, First Minister-designate) was totally in control of events.
"Nor can we at any time choose the situation that we are dealing with. We have to at all points respond to the actual situation which we are in." He added: "You can't start from an imagined or idealised position. You have to start from where you are in terms of reality."
It had been simple enough to deal with the situation when the republican movement was engaged solely in terrorism. But now republicans had opted for a different political approach and responding to this posed a challenge for unionists.
Faced with the slow decline of its campaign, the republican movement decided, in Mr Trimble's words, to "try and cash it in for some political advantage".
How to respond to this challenge? What he called "another unionist party" (presumably the DUP) would, he alleged, merely posture and set out "idealist, impossibilist, fundamentalist positions". But that was withdrawing from reality to become a party of permanent opposition. The strategy of presenting a "stone face" and saying "no" all the time was adopted in the past and it led to the Anglo-Irish Agreement. "It's not good enough simply to be passive," Mr Trimble said. At the end of the day, "the only sensible thing is to be seriously engaged in the situation that you are in".
Although Mr Trimble reiterated his views on decommissioning as a precondition for Sinn Fein involvement in the Northern executive, the broad thrust of his contribution left one with the feeling that this obstacle, like others in the peace process, would be overcome in due course.
One could argue that the biggest change since that small band of demonstrators set out in Derry 30 years ago today is that now unionists are beginning to work with nationalists to solve common problems instead of reacting in a defensive manner to a perceived threat to their position.
Although he did not use the phrase, in essence Mr Trimble was telling his young troops on Saturday that the siege mentality was no longer appropriate. Thirty years on, there may at last be grounds for hope.