Ever hear this one? "Atheists have a problem. They can't explain where the universe came from. You can't create something from nothing, and that's a big problem for atheism."
It's a common and bewildering notion that atheists need to be able to explain every mystery in the universe before making the audacious suggestion that maybe there isn't an invisible magic man in the sky.
Ok, so I don't know where the universe came from. I don't know why there's something rather than nothing. But why would my lack of knowledge conflict with my lack of belief? Ignorance and disbelief go together perfectly. In fact, one logically follows from the other. If I don't know what caused the universe, then I don't believe in any particular explanation. I'm open to the possibility that a god created it, as well as other possibilities, but I'm not going to settle for any particular explanation without proof. To put it as simply as I can, I don't know that God created the universe, so I don't believe that God created the universe.
In a Venn diagram of a rational person's mind, knowledge and belief should be indistinguishable. They should be right on top of each other, not just overlapping. To know without believing is denial, and to believe without knowing is faith.
If we are honestly seeking the truth, we won't find it by inventing magical explanations for things we don't understand. The existence of the universe doesn't prove a god anymore than presents under a tree prove Santa Clause. Just because we don't know how it got there, doesn't mean there has to be a supernatural being who put it there.
The fact that I don't know where the universe came from is not a problem for me, because I'm not the one claiming to know where the universe came from. The problem is with theists who claim the universe came from a god, but have no proof.