But you know the example of the guy without a quarter of a brain, lost in an accident, still functioning normally, as years later the doctors said that the other parts of the brain got in and adapted to compensate for the missing one.
We have to be careful with what "normal" is in these cases. I still test average or above on cognitive tests, yet I am well below where I was in several aspects. This heavily affects my capabilities. I don't know what the people without parts of their brains do for work, but "functioning normally" can often be considered being able to make it through a normal day.
I have never read the Alchemist. I actually don't read much non-fiction anymore as it is not enjoyable, it is heavy work. If I don't manually create the images from the text, I get nothing from it, and if I do create the images, it is very tiring. Another thing that has been lost :)