Why?

I think it falls on the beliefs of those that raised me. They didn't force their belief of God upon me, but I took on that belief as I questioned and learned from them.

That's another reason why I chose to believe (and still do believe) that there is a God and a after-life. That belief wasn't forced upon me, my parents allowed me to chose what I wanted to believe. I'm more inclined to listen to something if it isn't forced.

Simply, I believe it boils down to our experiences. Today I could be a believer, but tomorrow I could be an atheist. Some experiences in our lives can make enough of an impact to drastically change our ideals, and some experiences have little effect.

But, just like anything, we'll never really know until the end.