Unless you've studied psychology or psychobiology, you probably assume that the human brain is a rational operator, and even people that are crazy are basically the same as everyone else. This is an easy assumption to make, as far as most people can tell, they make decisions on a rational basis.
Unfortunately, humans are anything but rational, and deviance in brain function can be more profound than you can imagine.
Many decisions that human beings made are only explained after the fact. To test this, test subjects were given electrical impulses to force motion, or given psychological "triggers" that would provoke some physical response. After doing something inherently irrational, subjects inevitably came up with "reasons" why they did this, even though they hadn't decided to do it in the first place. Imagine how profoundly deceived humans can be when we can convince ourselves, for no reason, that we decided to do something when we were compelled to against our will.
People who suffer severe brain damage can gain a new worldview that seems impossible. Oliver Sacks, a neurobiologist, has written several books on the subject. There is a woman who has suffered brain damage that has deleted her perception of the direction "Left". Somehow, she is only able to perceive the right half of her world, only applying makeup to the right half of her face, and only eating the food on the right half of her plate. To see if there is any food on her plate she missed, she must turn nearly 360 degrees to the right to recenter the plate slightly to the left.
There are those who have suffered damage to the areas of the brain responsible for sight, and have been rendered completely blind, but still believe that they can see. Despite constant failures in their imagined "vision", they are adamant. On the other side of the coin, there are those who have suffered damage to the same general area, and lose the entire concept of sight. They cannot imagine the appearance of pictures, places, or people. The entire visual world is simply gone, as thoroughly as if they had never seen at all.
Anyway, Sack's books are interesting, so check them out if you like odd psychological problems. It's odd to see the common lack of interconnectedness in hospitals in his books. He'll find a case, assume it's unique because he's never seen it before, and write a paper, only to find out that there are dozens of cases that hadn't received much attention previously. I suppose in the world of the Internet, this information is more widespread, but if not, these things need to be on the Web. We should be treating people like this with as much information as possible.