The Road to Apostasy Is Paved With Bad Expectations
Recently, I was reading a Masters thesis by a Canadian student at the University of Toronto that focused on the experience of deconverting from Christianity to atheism. 
She made several observations that I thought were interesting:
A common pattern that emerges in deconversion stories is that an emotional / experiential shift occurs which paves the way for an intellectual reappraisal of beliefs.
When faith is strong, it is easy for people to ignore many of the intellectual challenges to their beliefs. But if an emotional factor came into play – such as being frustrated with God or feeling far from Him – they were more likely to passively consider faith threatening information.
Deconverts did not become receptive to faith threatening knowledge until they had reached a high level of frustration or emotional disconnect from their faith.
Many reported feeling frustration at and betrayal by God for not fulfilling certain expectations. Others felt wounded by the Church and could not distance God from it.
Once an initial emotional shift had occurred it established doubt or disillusionment. It was then deconverts began to think in new ways about their beliefs. Many of those beliefs became open for debate.
Finally, there is difference between a loss of faith and a loss of belief. Loss of faith is associated with emotional shifts. Faith, is understood as trust in and loyalty to God and is weakened by feelings of frustration, abandonment, disillusionment and apathy. Belief, is the state of being convinced of the truth of something. It is undermined by the evaluation of evidence. The loss of faith often leads to the loss of belief.
In summary, many former believers trace the beginning of their loss of faith not to reason but to emotion. The negative emotions which precipitated their revaluation of the evidence for Christianity often was the result of having expectations of God which were unmet. Feeling He let them down, that He didn’t care, or that He had not fulfilled certain promises was enough to allow them contemplate intellectual issues that were already in the back of their minds.
Why I find her results so interesting is because many atheists maintain that atheism is the result of the deliverances of dispassionate reason. The claim is often made by atheists that if believers would just reason rightly they too would become atheists. However, it seems that the argument could be turned on its head, “If you former Christians were more reasonable and less influenced by your emotions you would still be believers!” C.S. Lewis long ago noted the danger of negative emotions to a reasoned faith. And of course he said it better:
Roughly speaking, the word faith seems to be used by Christians in two senses or on two levels, and I will take them in turn. In the first sense it means simply belief--accepting or regarding as true the doctrines of Christianity. That is fairly simple. But what does puzzle people--at least it used to puzzle me--is the fact that Christians regard faith in this sense as a virtue. I used to ask how on Earth it can be a virtue--what is there moral or immoral about believing or not believing a set of statements? Obviously, I used to say, a sane man accepts or rejects any statement, not because he wants or does not want to, but because the evidence seems to him good or bad. If he were mistaken about the goodness or badness of the evidence, that would not mean he was a bad man, but only that he was not very clever. And if he thought the evidence bad but tried to force himself to believe in spite of it, that would be merely stupid.
Well, I think I still take that view. But what I did not see then--and a good many people do not see still--was this. I was assuming that if the human mind once accepts a thing as true it will automatically go on regarding it as true, until some real reason for reconsidering it turns up. In fact, I was assuming that the human mind is completely ruled by reason. But that is not so. For example, my reason is perfectly convinced by good evidence that anesthetics do not smother me and that properly trained surgeons do not start operating until I am unconscious. But that does not alter the fact that when they have me down on the table and clap their horrible mask over my face, a mere childish panic begins inside me. I start thinking I am going to choke, and I am afraid they will start cutting me up before I am properly under. In other words, I lose my faith in anesthetics. It is not reason that is taking away my faith; on the contrary, my faith is based on reason. It is my imagination and emotions. The battle is between faith and reason on one side and emotion and imagination on the other.....
Now just the same thing happens about Christianity. I am not asking anyone to accept Christianity if his best reasoning tells him that the weight of evidence is against it. That is not the point at which faith comes in. But supposing a man's reason once decides that the weight of the evidence is for it. I can tell that man what is going to happen to him in the next few weeks. There will come a moment when there is bad news, or he is in trouble, or is living among a lot of other people who do not believe it, and all at once his emotions will rise up and carry out a sort of blitz on his belief. Or else there will come a moment when he wants a woman, or wants to tell a lie, or feels very pleased with himself, or sees a chance of making a little money in some way that is not perfectly fair; some moment, in fact, at which it would be very convenient if Christianity were not true. And once again his wishes and desires will carry out a blitz. I am not talking of moments at which any real new reasons against Christianity turn up. Those have to be faced and that is a different matter. I am talking about moments where a mere mood rises up against it.
Now faith, in the sense in which I am here using the word, is the art of holding onto things your reason has once accepted, in spite of your changing moods. For moods will change, whatever view your reason takes. I know that by experience. Now that I am a Christian, I do have moods in which the whole thing looks very improbable; but when I was an atheist, I had moods in which Christianity looked terribly probable. This rebellion of your moods against your real self is going to come anyway. That is why faith is such a necessary virtue; unless you teach your moods "where they get off" you can never be either a sound Christian or even a sound atheist, but just a creature dithering to and fro, with its beliefs really dependent on the weather and the state of its digestion. Consequently one must train the habit of faith.
C.S Lewis, Mere Christianity
I can’t add anything to what Lewis has said. But I do think it is worth noting that what causes many folks, including Lewis himself, to be open to doubt are unfulfilled expectations that they have of God. I have seen this principle play out in my own life. Rarely is it an argument or some new bit of evidence against the Faith that causes me to doubt. Rather, it is more often than not, a feeling of frustration or anger, due to God not meeting one of my expectations of Him. When that happens, I find myself entertaining the tensions within my worldview that for the most part I am willing to ignore.
All of this raises the question, “What can we reasonably expect from God?” Because if people come to believe in God and subsequently develop unrealistic expectations of what He will do for them, they will be set up for a major crisis of faith. I am persuaded that in many cases, deconverts have been set up for their loss of faith by the very churches that thought they were nourishing their faith. Instead they provided them with a false understanding of God and what He has promised us. This paved the way for them to become disillusioned with, and feel let down by God. Ultimately, they ended up losing their belief in His existence and became atheists.
Our expectations of who God is and what He has promised us are important. They need to be in accord with the Bible, because if they are significantly out of line with Scripture, the consequences can be monumental.
 Karen Heather Ross, Losing Faith in Fundamentalist Christianity. OISE, University of Toronto, (2009).