I think we were all so shocked by his death that it took a long time for us to accept that a new world order had been put in motion.
I had just turned 12 when it happened, and it was just so unbelievable that the US President had been assassinated in the US itself, and by person or persons unknown, not by a foreign power, but by an American (or two or three).
I think the world changed that day, from one of optimisim for the future, to one of sadness and pessimism. Kennedy for us in the UK was a breath of fresh air. A new young handsome man, with massive charisma and charm, who seemed to embody for us all that was good about the free world. He was the President who seemed to represent all of our hopes and aspirations, no matter which country we lived in, and we loved him.
So to see him murdered, live on TV was absolutely terrible. It was as though the devil himself had declared war on ordinary decent human society, and not only was injustice done, it was demonstrably seen to be done. Seemingly as a way of demoralising us all into submission to the new normal of hatred and death.
FDR said that December 7th would live on in infamy. I think that Nov 22nd will as well, for those of us who were alive at the time. It's been a stain on society ever since, that not only did it happen, but that Americans allowed it to happen, and didn't immediately root out the conspirators who'd carried out JFKs execution. As to those who maintained it was a lone gunman, I think we all knew immediately that more than one person was involved, so it was an insult to our intelligence to present us with a patsy in the form of Oswold, and then the theatre of having him murdered live on TV by Ruby.