The Power of Unbelief

What is the worst sin you've ever committed? Murder, rape, abortion? Maybe you've been guilty of gross indecency. Maybe you've directly blasphemed God.
Let me put it another way: What is the most powerful sin you've ever committed? Of all your sins, which sin has greatest power to destroy your life and the lives of others? If we ask the Bible this question, I think the answer might surprise us.