If God is all knowing, then why did he create us in the first place if he knew we were going to "fall in sin"?
Why do we have kids? We know that will cause our life to change, they will cause us heart ache, that will hate us at times, and in the end they leave us.
We know that this world is screwed up and a terrible place to raise children but we still want them, why?
When you've answered these questions you'll know why God created us.