It's outside our experience until it starts to happen. We can intellectually process the concept of death (memento mori etc) but that is very different to our own experiences of our own demise.

I had a very close friend who was deeply interested in spirituality and philosophy and who devoted a good part of his life to understanding our existence. Nothing prepared him for the painful cancer death experiences he endured. Intellectual perceptions are nothing against our first and only viceral experiences of death....