Whenever I find myself in doubt over the existence of a tangible God - usually following the reading of another fallacious "let's put creationism in the classroom" article - I remind myself of a very famous mathematician and philosopher, Blaise Pascal. Pascal wagered that it behooves one to believe in God because the likelihood of being rewarded with hell is eliminated if they believe. A simplistic chart illustrating his wager is as follows:

------------------God Exists--------God Doesn't Exist-------
Believe --------Eternal Paradise----Purposeful Life, No Reward
Don't Believe -Eternal Damnation--Meaningless Life, No Reward

If you don't believe in God and God doesn't exist, then you likely live a less than happy life (for there's no heavenly reward for which you work hard). If you don't believe in God and God does exist, you will receive eternal damnation because you were indeed told to believe, but failed to have faith! However, if you believe in God and God doesn't exist, then you live a wholesome life with basically no reward in the end. If you believe in God and God does exist, then you have an eternal reward for your faith!

In other words, if you refuse to believe, the best you can hope for is nothing and the worse is eternal damnation: you can never come out ahead. But if you choose to believe, the worse you can expect is nothing and the best you can expect if eternal bliss: you have a 50/50 chance of winning! So, if you're mathematically inclined and have your doubts as to the veracity and likelihood of an ultimate, magnanimous God, your best bet is simply to choose to believe and live like it.

For me, in my daily struggle to contemplate the existence of a benevolent deity in a world filled with malevolence and indifference, I choose to simply believe if for no other reason than Pascal's Proof.

How do you rationalize your own belief or lack thereof?

(Thanks to http://plato.stanford.edu/entries/pascal-wager/ for a useful reference.)