Are You 100% Sure God Exists?

I talked with someone this week who said he was 100% sure God existed. I found that to be an interesting statement. 100% sure. What does anyone think he meant by that? What other beliefs do Christians have that are 100% sure? Can a Christian admit he or she is only, say, 75% sure God exists? Why/Why not? Is a Christian more sure God exists than other things that are obvious? Which kinds of things? How does what you believe as a Christian compare with the other things you believe? Why would anyone feel the need to claim he is 100% sure that God exists?