Recently I've been saying that it is important to distinguish between what people believe, what they say they believe and what they do. The three do not always integrate well together. One can posit many reasons for this, though I believe some form of cognitive modularity and various social psychological pressures can probably account for much of it. It seems a trivial and obvious point, but in discussions about human motives and predictions about their behavior these issues tend to be ignored. The problem is that people have a hard time treating other human beings as natural objects. There's a reason for this, we're damn complicated and hard to figure out. Additionally, our intuitive psychology gives us a lot of "free information" concealed within our heads which we take for granted, we don't have to make recourse to explicit models because we know much of what needs to be known implicitly. We trust introspection because it works well in day to day interactions, we come preloaded with a lot of people interpretation software.

I bring this up because I was remembering a stupid thing I used to say about religious people: if the religious believe in an afterlife why do they get so scared when people are about to kill them? This was a dumb "gotcha" for showing that religious people weren't really that religious, that they didn't really believe that there was an afterlife because they didn't behave as if there was an afterlife when this life was going to get snuffed out. I've seen this come up on the message boards here too, I'm not the only person who has naively expressed this truth as if it's clever.

The problem is that we assume that people are cognitively integrated, and that there is a tight fidelity between their various beliefs and how they inform one's actions. And, reflectively, if one accepts that evolution has shaped our behavorial suite to some extent, reflexive fear of getting killed would seem to be one of the most adaptive handy mental biases! I was always a big fan of evolutionary psychology, but I was too much a moron to consider this. That is, even if someone sincerely believed that there was a life after, their "instinct" for fear would simply overwhelm their reflective beliefs in the "heat of the moment." Obviously if you didn't have this "flight or fear" sort of instinct, not matter your prior beliefs about the afterlife (most peoples seem to have some expectation of post-mortem sentience, though it usually isn't as cheery as modern religions make it out to be), your long term fitness will decrease. Ultimately you could probably think it through and come to the conclusion that it is best to run and hide, but by that time you might be dead.

Addendum: You can invert this with the "there are no atheists in a foxhole" saying, just because someone makes recourse to divine aid in a moment of duress doesn't mean they rationally believe said being exists. Many unbelievers I know have a strong bias toward wishing there was a divine being, they simply can't reflectively convince themselves that its existence is plausible. It makes sense that native cognitive biases can shunt aside reflection in situations where cost of philosophical inconsistency seems trivial. This sort of in-the-moment apostacy is well known in in religious circles, the Donatist movement in ancient Rome arose because so many Christians, including bishops and church leaders, had apostasized under threat of persecution and death. The orthodox position was that apostates had to be forgiven because of considerations of human nature, while the Donatists rejected such compromises. The reality is that the apostates were almost certainly sincere Christians, they often reverted back the first chance they got, but they also had a strong instinctive fear of death, so they compromised their principles.