Why it is hard to imagine there being no afterlife.
Now if you think about it logically and objectively, it doesn't seem that difficult. What's wrong with a consciousness ending, never to continue? Subjectively, however, it's a whole different situation.
The first problem is to make sure people aren't trying to think of the wrong thing. Often people talk about what it would be like without an afterlife in terms of a black void or somesuch. But that's incorrect. A black void, or a blue void, or even a plaid void is still a something. No afterlife would mean absolutely nothing.
Now, it couldn't be unpleasant, because for something to be that way requires you to experience it. But with no afterlife, there's no awareness, no consciousness to experience with. The closest we can come to that state would be unconsciousness, like that created suring surgery. Without the consciousness, there is no way to detect the passage of time, so it all goes by in an instant - you travel from the beginning of that time to the end instantly, from your vantage point.
But because no afterlife means you're dead and unconscious forever, there is no end point. The state goes on for eternity. But if, like with the surgery example, it all travels by in an instant, wouldn't that eternity also travel by in an instant, leaving you at the end? It seems like a paradox that you can't resolve. Forever passing by instantaneously?
I have yet to resolve this in my mind. It doesn't prevent me from not believing in an afterlife, but it doesn't make it easy.