I see a road sign. I read its message, be it speed limit or a mile marker. I assume, before I pass it, that the sign has another side. In my rear-view mirror, I can confirm it did have another side: It was blank and the signpost was exposed. My assumption that there is another side has always been right. This is confidence.
So one may (errantly) argue an equal confidence that life, too, has another side. They would see it as a logical jump from one assumption to the other. If a sign always has two sides, then life must also always have two sides.
The point of death exists, and it must usher in something else equal to life, its mirror image manifested in the afterlife. Why would one not make this assumption the way one can assume it with the road sign?
Well, the one thing I cannot do without firsthand knowledge is verify the existence of any kind of an afterlife -- not until I die and experience the afterlife for myself (or don't) firsthand would I be able to say with confidence whether or not any afterlife exists. I have no more confidence in this, due to a lack of verifiable evidence of this, than anybody else who hasn't experienced it firsthand.
And if there is no afterlife, I wouldn't be able to say it. I would simply cease to exist, along with my consciousness, my sentience. My body would be buried and return to the soil, providing nutrients for plants and, perhaps, bugs, livestock, humans, etc. The circle of life continues on earth while my awareness ceases to exist.
My existence is exactly as finite as my life. It had a beginning point; this must be true because I don't remember anything from before I was born. The mirror image here is not an afterlife; the mirror image is life's other endpoint: death.
