If you remember back when Queen Elizabeth II died, how upset most British people were and how it caused some social insecurity as many British people saw her as a sense of strength and a rock due to her continuity and longevity, but with her gone, they weren't sure how Britain would fare. Hence, the large crowds of mourners and a lot of upset.
King Charles III - though not as admired as Queen Elizabeth was - also has longevity and a sense of continuity in a different way: not as monarch since he's only been in the role for three years, but as a royal figure, i.e. he has been in the spotlight since the 1940s and conducting royal duties since the 1960s. When he dies, will Britain finally feel as though the older generation of royals - who for so long have provided reassurance and comfort to the British people - have gone?
Will this lead to a lot of soul-searching about where next Britain must go and perhaps cause social tensions due to the insecurity of identity? Who will the British look to to guide the nation from then on? Who will be their new rock?