This is an egregious over simplification of religious belief. I think most religious people are absolutely not 100% sure. That's why faith is such a big topic,

This is an egregious over simplification of religious belief. I think most religious people are absolutely not 100% sure. That's why faith is such a big topic, and why philosophers and theologians have written about faith, the existence of god, whether it can be proven, etc. for centuries. Besides, aren't all your actions based on beliefs that are are less than 100% certain? I don't know that the line of code I'm writing is going to compile, or that the company I'm working for isn't going to go under tomorrow, or that the relationships I'm investing time into are going to last forever, but I'm certain enough that I proceed with them. Believing in God isn't so different.