Joan Didion famously wrote that "Life changes in an instant" - and so it did for Northern Ireland shoppers on June 20, 1995.
That was the day when David Sainsbury (now Lord Sainsbury of Turville) came to Belfast to announce ambitious plans for the development of a chain of supermarkets here.
Sainsbury promised that he would open seven new-build stores within two years and that, by the beginning of the millennium, he would have a chain of 20 supermarkets in Northern Ireland.
Twenty years later, he must be somewhat disappointed if he ever sits back and reflects on the progress of his company because - to date - he has only 13 stores here.
The arrival of Sainsbury's in Northern Ireland was a long, slow and arduous route to market as many of the stores it planned to open were on greenfield sites, which upset the-then indigenous chains Stewarts, Crazy Prices and Wellworths, and became the subject of sometimes lengthy, tricky and protracted public planning inquiries.
In the meantime, Tesco played a very different game. It cleverly acquired the Associated British Foods empire (north and south), as it had done previously in Scotland with the William Low supermarket chain and, as a result, stole a march on Sainsbury's.
On June 19, 1997, Safeway chose a third entry route by signing a joint venture agreement with Wellworths before selling out to Morrisons, who had a very short tenure in Northern Ireland.
Morrisons came and saw, but never conquered. Its exit left room for Asda to move in to provide consumers with the opportunity to shop with another of the Big Four supermarket chains.
It all seems a long time ago and yet, in the 20 years between June 1995 and now, the Northern Ireland retail food sector has changed irrevocably and beyond all recognition - both institutionally and structurally.
Few would argue that the changes have not been good for consumers, but Sainsbury's must feel at least marginally disappointed with its limited number of outlets - especially given its initial grandiose plans of 20 years ago. Thirteen: unlucky for some.