For instance, a religious man may firmly believe that his god is as real as he is, if not more, constantly watching over him, and eager to reward the faithful beyond their wildest dreams. Still, given a brief opportunity to be faithless, he will then act as if he had never heard ofany god, much less any reward for keeping faith.
Conversely, there are sworn materialists who firmly believe that there is no free will and that life has no purpose beyond passing on your genes to another generation. Yet they will day by day act and feel as if they had free will and their life had a higher purpose.
These are merely extreme examples. Overall, the detachment of head from heart (symbolically speaking of course) is one of the most remarkable traits of the human race. If a rational species were to think up imaginary creatures to populate a fictional universe, they would probably never in their lifetime come up with such an outrageous idea.