Perhaps, if you are a theist, you might not want to read this. If you are nevertheless curious about how an atheist thinks, then please read on.
I don't think there are any active members of this board who have been atheists all their lives (are there?). I think virtually all of us transitioned into non-belief from a religious beginning. Some were born-ins, others drifted in then out, still others who like me never took the plunge but who came ever so close. At one point in our lives we believed in God and a purpose of life.
Perhaps the hardest thing to accept on becoming atheist is the clear realisation that everyone loses his or her place in the sun. Not temporarily. Forever. This an atheist comes to accept on the basis of the evidence of history, the evidence of science and the evidence of his eyes. Contrast this belief with that of a present day Jehovah's Witness. He or she has an expectation that
a) they have a chance at never having to die at all (which would be a really, really good thing), and
b) even if they do die they're going to be resurrected into a perfect, young body and live in peace and harmony on paradise earth forever and ever.
Once you realise that a) just isn't going to happen - no rapture, no post-Armageddon - you're left with a belief that is every bit as irrational. There's another flavour of b) that goes something like, yes, everyone dies in body, but their sprit lives on for all eternity.
Here's were the dichotomy happens. Once you start on the road to atheism and insist on learning about things that are substantiated by evidence and observation it becomes more and more difficult to believe a) or b), or whatever flavour of b). At the same time, you still want to believe at least some variant of b), because it is hard to contemplate that you and your loved ones, beginning at some point in the very near future, will never see one another again. The undeniable fact of the matter is your future awaits. It could be soon, it could be many years away, but next to eternity it is not even a blink of time. You will either die from trauma or disease of some kind or slowly by decrepitation. And then the lights just go out. For a theist, as I once was, it is a frightening thing even to contemplate, let alone make a concerted attempt to understand. But that understanding eventually does come when you finally put aside what you are afraid of.
And then you find peace and you find wonderment in learning about and understanding how the world really works. The truth is far, far more fascinating and enthralling than any of those ancient fables.