http://entertainment.gather.com/viewArticle.action?articleId=281474978103767

Let's assume for the moment that the true nature of freedom is choosing the circumstances by which you are born into this life, rather than the ability to exert unlimited power in this life.

By coming here to this life, you deliberately decided to impose a vast swath of restrictions on yourself. You are caught up in this river of thought that includes things like the physical laws, laws such as the ones that govern the nature of chemical reactions, the movement of celestial bodies, and the passage of time. In addition, your life choice dictated, in general terms, your economic status, the color of your skin, and your general intelligence level.

Why would we do this? Maybe for the same reasons we go to see a movie. In a sense, a movie is a metaphor for a lifetime (even though it only lasts for 2 hours):

"You can hold a reel of film in your hands," he said, "and it's all finished and complete - beginning, middle, end are all there that same second, the same millionths of a second. The film exists beyond the time that it records, and if you know what the movie is, you know generally what's going to happen before you walk into the theater: there's going to be battles and excitement, winners and losers, romance, disaster; you know that's all going to be there. But in order to get caught up and swept away in it, in order to enjoy it to its most, you have to put it in a projector and let it go through the lens minute by minute...any illusion requires space and time to be experienced. So you pay your nickel and you get your ticket and you settle down an forget what's going on outside the theater an the movie begins for you."

-- Richard Bach, "Illusions: The Adventures of a Reluctant Messiah"

So the right question to ask might be: Why would a person who is mentally challenged have decided to enter life in this way?

Could it be that he had something to learn from the struggle? Or that others might have something to learn from him?