We choose a certainty of failure over a chance at success because we like certainty more than we like success.
First, the negative theology of fear, so that we can see why we have made our mistake:
Suppose that you were given two choices: either you could be injured straight away and be done with it, or else you could be tracked down by a pursuer and injured whenever he found you. However, this pursuer would give up if he could not find you within the day.
Now imagine that instead of one day, your ordeal was drawn out across three.
Provided that the stakes are sufficiently high, my inclination to accept the second option decreases as the length of time increases, because of anxiety. I know that during the time I spend waiting, I will worry constantly that my pursuer may catch me at any moment. Over a long enough period of time, the pain of carrying this fear becomes stronger than the pain of the injury itself- even though that injury is the object of my fear. I would rather be injured than fear injury. The result of my worrying is that the fear of anxiety, that is, the fear of fear, leads me to choose the first option even though it is the second which creates the possibility of avoiding injury. But my entire reason for worrying was that I wanted to avoid injury; I worried because I did not want to be injured. Anxiety is therefore a failure on its own terms: if it is necessary then it is ineffective, if it is effective then it is unnecessary.
The basic error is our inclination towards worrying, and its result is fear of fear, which inspires acts of nihilism. Although fear is on its face a perfectly reasonable response to danger, the fact that we do not like being afraid is enough reason for us not to be- else our fear will lead us into greater danger.
So the atheist does not disbelieve in God because he does not want for there to be a God; he disbelieves in God because he does want for there to be a God. And the believer does not avoid allowing God to mean anything to him because he loves meaninglessness; he does it because he despises meaninglessness.
Our ultimate goal is to rid ourselves of nihilism in the risk-reward analysis which we undertake in the consideration of our ultimate good, but to do so we must identify and learn to countermand the inclination towards worrying about our ultimate good.