One of the most interesting results to come out of this study was that the intellectually based reasons of "good design" and "experience of God," which were in first and second place in the first question of Why do you believe in God?, dropped to sixth and third place for the second question of Why do you think other people believe in God? Taking their place as the two most common reasons other people believe in God were the emotionally based categories of "comforting" and "raised to believe."
Michael Shermer, How We Believe: Science, Skepticism, and the Search for God (Second Edition), Owl Books, 2003. p.85
Shermer goes on to suggest that the reason for this is an attribution bias--we tend to view ourselves as rational, and others as emotional. I'd take it a step farther than that, and suggest we tend to see in others a reflection of self, while insight is--as Loren Rosson often points out--quite frequently self-deception.